O que há de novo no Python 2.7¶

Autor:: A.M. Kuchling (amk at amk.ca)

Este artigo explica os novos recursos do Python 2.7. O Python 2.7 foi lançado em 3 de julho de 2010.

A manipulação numérica foi aprimorada de várias maneiras, tanto para números de ponto flutuante quanto para a classe Decimal. Existem algumas adições úteis à biblioteca padrão, como um módulo unittest bastante aprimorado, o módulo argparse para analisar as opções da linha de comando, classes convenientes OrderedDict e Counter no módulo collections e muitas outras melhorias.

O Python 2.7 está planejado para ser o último dos lançamentos 2.x, por isso trabalhamos para torná-lo um bom lançamento a longo prazo. Para ajudar na migração para o Python 3, vários novos recursos da série Python 3.x foram incluídos no 2.7.

Este artigo não tenta fornecer uma especificação completa dos novos recursos, mas fornece uma visão geral conveniente. Para detalhes completos, você deve consultar a documentação do Python 2.7 em https://docs.python.org. Se você deseja entender a lógica do design e implementação, consulte a PEP para obter um novo recurso específico ou o problema em https://bugs.python.org no qual uma alteração foi discutida. Sempre que possível, o “O que há de novo no Python” é vinculado ao item de bug/patch de cada alteração.

O futuro para o Python 2.x¶

Python 2.7 é o último grande lançamento da série 2.x, já que os mantenedores do Python mudaram o foco de seus esforços de desenvolvimento de novos recursos para a série Python 3.x. Isso significa que, embora o Python 2 continue recebendo correções de bugs e seja atualizado para construir corretamente em novo hardware e versões de sistemas operados com suporte, não haverá novos lançamentos de recursos completos para a linguagem ou biblioteca padrão.

No entanto, embora haja um grande subconjunto comum entre Python 2.7 e Python 3, e muitas das mudanças envolvidas na migração para esse subconjunto comum, ou diretamente para Python 3, podem ser automatizadas com segurança, algumas outras mudanças (principalmente aquelas associadas ao tratamento Unicode) pode exigir uma consideração cuidadosa e, de preferência, conjuntos de testes de regressão automatizados robustos, para migrar com eficácia.

Isso significa que o Python 2.7 permanecerá em vigor por um longo tempo, fornecendo uma plataforma base estável e com suporte para sistemas de produção que ainda não foram portados para Python 3. O ciclo de vida completo esperado da série Python 2.7 é detalhado na PEP 373.

Algumas consequências principais da significância de longo prazo de 2.7 são:

Conforme observado acima, a versão 2.7 tem um período de manutenção muito mais longo em comparação com as versões 2.x anteriores. Atualmente, espera-se que o Python 2.7 continue com o suporte da equipe de desenvolvimento central (recebendo atualizações de segurança e outras correções de bugs) até pelo menos 2020 (10 anos após seu lançamento inicial, em comparação com o período de suporte mais típico de 18-24 meses).
Conforme a biblioteca padrão do Python 2.7 envelhece, fazer uso efetivo do Índice de Pacotes do Python (diretamente ou por meio de um redistribuidor) torna-se mais importante para os usuários do Python 2. Além de uma grande variedade de pacotes de terceiros para várias tarefas, os pacotes disponíveis incluem backports de novos módulos e recursos da biblioteca padrão do Python 3 que são compatíveis com o Python 2, bem como várias ferramentas e bibliotecas que podem tornar mais fácil migre para Python 3. O Python Packaging User Guide fornece orientação sobre como baixar e instalar software do Índice de Pacotes Python.
Embora a abordagem preferida para aprimorar o Python 2 agora seja a publicação de novos pacotes no Índice de Pacotes do Python, essa abordagem não funciona necessariamente em todos os casos, especialmente aqueles relacionados à segurança de rede. Em casos excepcionais que não podem ser tratados adequadamente com a publicação de pacotes novos ou atualizados no PyPI, o processo de Proposta de Melhoria do Python (PEP) pode ser usado para justificar a adição de novos recursos diretamente à biblioteca padrão do Python 2. Quaisquer adições, e as versões de manutenção onde foram adicionadas, serão observadas na seção New Features Added to Python 2.7 Maintenance Releases abaixo.

Para projetos que desejam migrar de Python 2 para Python 3, ou para desenvolvedores de bibliotecas e frameworks que desejam oferecer suporte a usuários em Python 2 e Python 3, há uma variedade de ferramentas e guias disponíveis para ajudar a decidir sobre uma abordagem adequada e gerenciar alguns dos os detalhes técnicos envolvidos. O ponto de partida recomendado é o guia Como portar códigos do Python 2 para o Python 3.

Mudanças no tratamento de avisos de descontinuação¶

Para Python 2.7, uma decisão política foi feita para silenciar avisos apenas de interesse para desenvolvedores por padrão. DeprecationWarning e seus descendentes agora são ignorados a menos que solicitado de outra forma, evitando que os usuários vejam avisos acionados por uma aplicação. Essa mudança também foi feita no branch que se tornou o Python 3.2. (Discutido em stdlib-sig e realizado em bpo-7319.)

Em versões anteriores, as mensagens DeprecationWarning eram habilitadas por padrão, fornecendo aos desenvolvedores de Python uma indicação clara de onde seu código pode quebrar em uma versão principal futura do Python.

No entanto, há cada vez mais usuários de aplicações baseadas em Python que não estão diretamente envolvidos no desenvolvimento dessas aplicações. Mensagens de DeprecationWarning são irrelevantes para tais usuários, fazendo-os se preocupar com uma aplicação que está realmente funcionando corretamente e sobrecarregando os desenvolvedores de aplicações com a resposta a essas preocupações.

Você pode reativar a exibição de mensagens DeprecationWarning executando Python com a opção -Wdefault (forma curta: -Wd) ou definindo a variável de ambiente PYTHONWARNINGS para "default" (ou "d") antes de executar o Python. O código Python também pode reativá-los chamando warnings.simplefilter('default').

O módulo unittest também reativa automaticamente os avisos de depreciação ao executar testes.

Recursos do Python 3.1¶

Assim como o Python 2.6 incorporou recursos do Python 3.0, a versão 2.7 incorpora alguns dos novos recursos do Python 3.1. A série 2.x continua a fornecer ferramentas para migração para a série 3.x.

Uma lista parcial de recursos do 3.1 que foram transferidos para o 2.7:

A sintaxe para conjuntos de literais ({1,2,3} é um conjunto mutável).
Compreensões de dicionário e conjunto ({i: i*2 for i in range(3)}).
Vários gerenciadores de contexto em uma única instrução with.
Uma nova versão da biblioteca io, reescrita em C para melhor desempenho.
O tipo de dicionário ordenado descrito na PEP 372: Adicionando um dicionário ordenado a coleções.
O novo especificador de formato "," descrito na PEP 378: Especificador de formato para separador de milhares.
O objeto memoryview.
Um pequeno subconjunto do módulo importlib, descrito sob.
O repr() de um ponto flutuante x é mais curto em muitos casos: agora é baseado na string decimal mais curta que é garantida para arredondar de volta para x. Como nas versões anteriores do Python, é garantido que float(repr(x)) recupera x.
As conversões de ponto flutuante para string e string para ponto flutuante são arredondadas corretamente. A função round() também está agora corretamente arredondada.
O tipo PyCapsule, usado para fornecer uma API C para módulos de extensão.
A função de API C PyLong_AsLongAndOverflow().

Outros novos avisos do modo Python3 incluem:

operator.isCallable() and operator.sequenceIncludes(), which are not supported in 3.x, now trigger warnings.
A opção -3 agora habilita automaticamente a opção -Qwarn que causa avisos sobre o uso de divisão clássica com inteiros e inteiros longos.

PEP 372: Adicionando um dicionário ordenado a coleções¶

Dicionários Python regulares iteram sobre pares de chave/valor em ordem arbitrária. Ao longo dos anos, vários autores escreveram implementações alternativas que lembram a ordem em que as chaves foram inseridas originalmente. Com base nas experiências dessas implementações, 2.7 introduz uma nova classe OrderedDict no módulo Collections.

A API OrderedDict fornece a mesma interface que os dicionários regulares, mas itera sobre chaves e valores em uma ordem garantida dependendo de quando uma chave foi inserida pela primeira vez:

>>> from collections import OrderedDict
>>> d = OrderedDict([('first', 1),
...                  ('second', 2),
...                  ('third', 3)])
>>> d.items()
[('first', 1), ('second', 2), ('third', 3)]

Se uma nova entrada substituir uma entrada existente, a posição de inserção original permanece inalterada:

>>> d['second'] = 4
>>> d.items()
[('first', 1), ('second', 4), ('third', 3)]

Excluir uma entrada e reinseri-la irá movê-la para o final:

>>> del d['second']
>>> d['second'] = 5
>>> d.items()
[('first', 1), ('third', 3), ('second', 5)]

O método popitem() tem um argumento opcional last cujo valor padrão é True. Se last for true, a chave adicionada mais recentemente é retornada e removida; se for falso, a chave mais antiga é selecionada:

>>> od = OrderedDict([(x,0) for x in range(20)])
>>> od.popitem()
(19, 0)
>>> od.popitem()
(18, 0)
>>> od.popitem(last=False)
(0, 0)
>>> od.popitem(last=False)
(1, 0)

A comparação de dois dicionários ordenados verifica as chaves e os valores e exige que o pedido de inserção seja o mesmo:

>>> od1 = OrderedDict([('first', 1),
...                    ('second', 2),
...                    ('third', 3)])
>>> od2 = OrderedDict([('third', 3),
...                    ('first', 1),
...                    ('second', 2)])
>>> od1 == od2
False
>>> # Move 'third' key to the end
>>> del od2['third']; od2['third'] = 3
>>> od1 == od2
True

Comparar um OrderedDict com um dicionário regular ignora a ordem de inserção e apenas compara as chaves e valores.

How does the OrderedDict work? It maintains a doubly linked list of keys, appending new keys to the list as they’re inserted. A secondary dictionary maps keys to their corresponding list node, so deletion doesn’t have to traverse the entire linked list and therefore remains O(1).

A biblioteca padrão agora suporta o uso de dicionários ordenados em vários módulos.

The ConfigParser module uses them by default, meaning that configuration files can now be read, modified, and then written back in their original order.
O método _asdict() para Collections.namedtuple() agora retorna um dicionário ordenado com os valores aparecendo na mesma ordem que os índices de tupla subjacentes.
O construtor de classe JSONDecoder do módulo json foi estendido com um parâmetro object_pairs_hook para permitir que instâncias OrderedDict sejam construídas pelo decodificador. O suporte também foi adicionado para ferramentas de terceiros como PyYAML.

Ver também

PEP 372 - Adicionando um dicionário ordenado às coleções: PEP escrita por Armin Ronacher e Raymond Hettinger; implementada por Raymond Hettinger.

PEP 378: Especificador de formato para separador de milhares¶

Para tornar a saída do programa mais legível, pode ser útil adicionar separadores a números grandes, renderizando-os como 18,446,744.073,709,551,616 em vez de 18446744073709551616.

A solução totalmente geral para fazer isso é o módulo locale, que pode usar diferentes separadores (“,” na América do Norte, “.” na Europa) e diferentes tamanhos de agrupamento, mas locale é complicado para usar e inadequado para aplicativos multithread onde diferentes threads estão produzindo saída para diferentes localidades.

Portanto, um mecanismo simples de agrupamento de vírgulas foi adicionado à minilinguagem usada pelo método str.format(). Ao formatar um número de ponto flutuante, basta incluir uma vírgula entre a largura e a precisão:

>>> '{:20,.2f}'.format(18446744073709551616.0)
'18,446,744,073,709,551,616.00'

Ao formatar um número inteiro, inclua a vírgula após a largura:

>>> '{:20,d}'.format(18446744073709551616)
'18,446,744,073,709,551,616'

Este mecanismo não é adaptável de forma alguma; vírgulas são sempre usadas como separadores e o agrupamento é sempre em grupos de três dígitos. O mecanismo de formatação de vírgula não é tão geral quanto o módulo locale, mas é mais fácil de usar.

Ver também

PEP 378 - Especificador de formato para separador de milhares: PEP escrita por Raymond Hettinger; implementada por Eric Smith.

PEP 389: O módulo argparse para analisar linhas de comando¶

O módulo argparse para analisar argumentos de linha de comando foi adicionado como um substituto mais poderoso para o módulo optparse.

This means Python now supports three different modules for parsing command-line arguments: getopt, optparse, and argparse. The getopt module closely resembles the C library’s getopt() function, so it remains useful if you’re writing a Python prototype that will eventually be rewritten in C. optparse becomes redundant, but there are no plans to remove it because there are many scripts still using it, and there’s no automated way to update these scripts. (Making the argparse API consistent with optparse’s interface was discussed but rejected as too messy and difficult.)

Resumindo, se você está escrevendo um novo script e não precisa se preocupar com a compatibilidade com versões anteriores do Python, use argparse ao invés de optparse.

Aqui está um exemplo:

import argparse

parser = argparse.ArgumentParser(description='Command-line example.')

# Add optional switches
parser.add_argument('-v', action='store_true', dest='is_verbose',
                    help='produce verbose output')
parser.add_argument('-o', action='store', dest='output',
                    metavar='FILE',
                    help='direct output to FILE instead of stdout')
parser.add_argument('-C', action='store', type=int, dest='context',
                    metavar='NUM', default=0,
                    help='display NUM lines of added context')

# Allow any number of additional arguments.
parser.add_argument(nargs='*', action='store', dest='inputs',
                    help='input filenames (default is stdin)')

args = parser.parse_args()
print args.__dict__

A menos que você o substitua, as opções -h e --help são adicionadas automaticamente e produzem uma saída formatada de maneira organizada:

-> ./python.exe argparse-example.py --help
usage: argparse-example.py [-h] [-v] [-o FILE] [-C NUM] [inputs [inputs ...]]

Command-line example.

positional arguments:
  inputs      input filenames (default is stdin)

optional arguments:
  -h, --help  show this help message and exit
  -v          produce verbose output
  -o FILE     direct output to FILE instead of stdout
  -C NUM      display NUM lines of added context

Como em optparse, as opções e argumentos da linha de comando são retornados como um objeto com atributos nomeados pelos parâmetros dest:

-> ./python.exe argparse-example.py -v
{'output': None,
 'is_verbose': True,
 'context': 0,
 'inputs': []}

-> ./python.exe argparse-example.py -v -o /tmp/output -C 4 file1 file2
{'output': '/tmp/output',
 'is_verbose': True,
 'context': 4,
 'inputs': ['file1', 'file2']}

argparse tem uma validação muito mais sofisticada que optparse; você pode especificar um número exato de argumentos como um inteiro, 0 ou mais argumentos passando '*', 1 ou mais passando '+', ou um argumento opcional com '?'. Um analisador de nível superior pode conter sub-analisadores para definir subcomandos que possuem diferentes conjuntos de opções, como em svn commit, svn checkout, etc. Você pode especificar o tipo de um argumento como FileType, que abrirá arquivos automaticamente para você e entende que '-' significa entrada ou saída padrão.

Ver também

Documentação do argparse: A página de documentação do módulo argparse.
Upgrading optparse code: Parte da documentação do Python, descrevendo como converter o código que usa optparse.
PEP 389 - argparse - Novo módulo de análise sintática de linha de comando: PEP escrita e implementada por Steven Bethard.

PEP 391: Configuração baseada em dicionário para logging¶

O módulo logging é muito flexível; os aplicativos podem definir uma árvore de subsistemas de log e cada logger nessa árvore pode filtrar determinadas mensagens, formatá-las de maneira diferente e direcionar mensagens para um número variável de manipuladores.

All this flexibility can require a lot of configuration. You can write Python statements to create objects and set their properties, but a complex set-up requires verbose but boring code. logging also supports a fileConfig() function that parses a file, but the file format doesn’t support configuring filters, and it’s messier to generate programmatically.

Python 2.7 adds a dictConfig() function that uses a dictionary to configure logging. There are many ways to produce a dictionary from different sources: construct one with code; parse a file containing JSON; or use a YAML parsing library if one is installed. For more information see Configuration functions.

O exemplo a seguir configura dois loggers, o logger raiz e um logger denominado “network”. As mensagens enviadas para o registrador raiz serão enviadas para o log do sistema usando o protocolo syslog, e as mensagens para o logger “network” serão gravadas em um arquivo network.log que será rotacionado assim que o log atingir 1 MB.

import logging
import logging.config

configdict = {
 'version': 1,    # Configuration schema in use; must be 1 for now
 'formatters': {
     'standard': {
         'format': ('%(asctime)s %(name)-15s '
                    '%(levelname)-8s %(message)s')}},

 'handlers': {'netlog': {'backupCount': 10,
                     'class': 'logging.handlers.RotatingFileHandler',
                     'filename': '/logs/network.log',
                     'formatter': 'standard',
                     'level': 'INFO',
                     'maxBytes': 1000000},
              'syslog': {'class': 'logging.handlers.SysLogHandler',
                         'formatter': 'standard',
                         'level': 'ERROR'}},

 # Specify all the subordinate loggers
 'loggers': {
             'network': {
                         'handlers': ['netlog']
             }
 },
 # Specify properties of the root logger
 'root': {
          'handlers': ['syslog']
 },
}

# Set up configuration
logging.config.dictConfig(configdict)

# As an example, log two error messages
logger = logging.getLogger('/')
logger.error('Database not found')

netlogger = logging.getLogger('network')
netlogger.error('Connection failed')

Três melhorias menores no módulo logging, todas implementadas por Vinay Sajip, são:

A classe SysLogHandler agora tem suporte a syslogging sobre TCP. O construtor tem um parâmetro socktype que fornece o tipo de soquete a ser usado, socket.SOCK_DGRAM para UDP ou socket.SOCK_STREAM para TCP. O protocolo padrão permanece UDP.
As instâncias Logger ganharam um método getChild() que recupera um logger descendente usando um caminho relativo. Por exemplo, depois de recuperar um logger fazendo log = getLogger('app'), chamar log.getChild('network.listen') é equivalente a getLogger('app.network.listen').
The LoggerAdapter class gained an isEnabledFor() method that takes a level and returns whether the underlying logger would process a message of that level of importance.

Ver também

PEP 391 - Configuração baseada em dicionário para logging: PEP escrita e implementada por Vinay Sajip.

PEP 3106: Views de dicionário¶

Os métodos de dicionário keys(), values() e items() são diferentes no Python 3.x. Eles retornam um objeto chamado view em vez de uma lista totalmente materializada.

It’s not possible to change the return values of keys(), values(), and items() in Python 2.7 because too much code would break. Instead the 3.x versions were added under the new names viewkeys(), viewvalues(), and viewitems().

>>> d = dict((i*10, chr(65+i)) for i in range(26))
>>> d
{0: 'A', 130: 'N', 10: 'B', 140: 'O', 20: ..., 250: 'Z'}
>>> d.viewkeys()
dict_keys([0, 130, 10, 140, 20, 150, 30, ..., 250])

As views podem ser iteradas, mas as exibições de chave e item também se comportam como conjuntos. O operador & realiza a interseção, e o | realiza uma união:

>>> d1 = dict((i*10, chr(65+i)) for i in range(26))
>>> d2 = dict((i**.5, i) for i in range(1000))
>>> d1.viewkeys() & d2.viewkeys()
set([0.0, 10.0, 20.0, 30.0])
>>> d1.viewkeys() | range(0, 30)
set([0, 1, 130, 3, 4, 5, 6, ..., 120, 250])

A view acompanha o dicionário e seu conteúdo muda à medida que o dicionário é modificado:

>>> vk = d.viewkeys()
>>> vk
dict_keys([0, 130, 10, ..., 250])
>>> d[260] = '&'
>>> vk
dict_keys([0, 130, 260, 10, ..., 250])

No entanto, observe que você não pode adicionar ou remover chaves enquanto estiver iterando na view:

>>> for k in vk:
...     d[k*2] = k
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: dictionary changed size during iteration

Você pode usar os métodos de exibição no código Python 2.x, e o conversor 2to3 irá alterá-los para os métodos padrão keys(), values() e items().

Ver também

PEP 3106 - Repaginação de dict.keys(), .values() e .items(): PEP escrita por Guido van Rossum. Backported para 2.7 por Alexandre Vassalotti; bpo-1967.

PEP 3137: O objeto memoryview¶

O objeto memoryview fornece uma visão do conteúdo da memória de outro objeto que corresponde à interface do tipo bytes.

>>> import string
>>> m = memoryview(string.letters)
>>> m
<memory at 0x37f850>
>>> len(m)           # Returns length of underlying object
52
>>> m[0], m[25], m[26]   # Indexing returns one byte
('a', 'z', 'A')
>>> m2 = m[0:26]         # Slicing returns another memoryview
>>> m2
<memory at 0x37f080>

O conteúdo da viewq pode ser convertido em uma string de bytes ou uma lista de inteiros:

>>> m2.tobytes()
'abcdefghijklmnopqrstuvwxyz'
>>> m2.tolist()
[97, 98, 99, 100, 101, 102, 103, ... 121, 122]
>>>

Objetos memoryview permitem modificar o objeto subjacente se for um objeto mutável.

>>> m2[0] = 75
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot modify read-only memory
>>> b = bytearray(string.letters)  # Creating a mutable object
>>> b
bytearray(b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
>>> mb = memoryview(b)
>>> mb[0] = '*'         # Assign to view, changing the bytearray.
>>> b[0:5]              # The bytearray has been changed.
bytearray(b'*bcde')
>>>

Ver também

PEP 3137 - Bytes imutáveis e buffer mutável: PEP escrita por Guido van Rossum. Implementada por Travis Oliphant, Antoine Pitrou e outros. Portado para 2.7 por Antoine Pitrou; bpo-2396.

Outras mudanças na linguagem¶

Alguma das mudanças menores feitas no núcleo da linguagem Python são:

A sintaxe para set literais foi portada do Python 3.x. Os colchetes são usados para cercar o conteúdo do conjunto mutável resultante; os literais definidos são diferenciados dos dicionários por não conterem caracteres de dois pontos e valores. {} continua a representar um dicionário vazio; use set() para um conjunto vazio.
```
>>> {1, 2, 3, 4, 5}
set([1, 2, 3, 4, 5])
>>> set() # empty set
set([])
>>> {}    # empty dict
{}
```
Portado por Alexandre Vassalotti; bpo-2335.
As compreensões de dicionário e conjunto são outro recurso importado do 3.x, generalizando as compreensões de lista/gerador para usar a sintaxe literal para conjuntos e dicionários.
```
>>> {x: x*x for x in range(6)}
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
>>> {('a'*x) for x in range(6)}
set(['', 'a', 'aa', 'aaa', 'aaaa', 'aaaaa'])
```
Portado por Alexandre Vassalotti; bpo-2333.
A instrução with agora pode usar vários gerenciadores de contexto em uma instrução. Os gerenciadores de contexto são processados da esquerda para a direita e cada um é tratado como o início de uma nova instrução with. Isso significa que:
```
with A() as a, B() as b:
    ... suite of statements ...
```
é equivalente a:
```
with A() as a:
    with B() as b:
        ... suite of statements ...
```
The contextlib.nested() function provides a very similar function, so it’s no longer necessary and has been deprecated.

(Proposta em https://codereview.appspot.com/53094; implementada por Georg Brandl.)
As conversões entre números de ponto flutuante (float) e strings agora são arredondadas corretamente na maioria das plataformas. Estas conversões ocorrem em muitos lugares diferentes: str() em floats e números complexos; os construtores float e complex; formatação numérica; serializar e desserializar floats e números complexos usando os módulos marshal, pickle e json; análise de float e literais imaginários no código Python; e a conversão Decimal-para-float.

Relacionado a isso, o repr() de um número de ponto flutuante x agora retorna um resultado baseado na string decimal mais curta que é garantida para arredondar de volta para x sob o arredondamento correto (com o modo de arredondamento round-half-to-even). Anteriormente, fornecia uma string baseada no arredondamento x para 17 dígitos decimais.

A biblioteca de arredondamento responsável por essa melhoria funciona no Windows e em plataformas Unix usando os compiladores gcc, icc ou suncc. Pode haver um pequeno número de plataformas onde a operação correta deste código não pode ser garantida, então o código não é usado em tais sistemas. Você pode descobrir qual código está sendo usado verificando sys.float_repr_style, que será short se o novo código estiver em uso e legacy se não estiver.

Implementada por Eric Smith and Mark Dickinson, usando a biblioteca dtoa.c de David Gay; bpo-7117.
As conversões de inteiros longos e inteiros regulares para ponto flutuante agora arredondam de maneira diferente, retornando o número de ponto flutuante mais próximo ao número. Isso não importa para pequenos inteiros que podem ser convertidos exatamente, mas para grandes números que inevitavelmente perderão a precisão, o Python 2.7 agora se aproxima mais. Por exemplo, o Python 2.6 computou o seguinte:
```
>>> n = 295147905179352891391
>>> float(n)
2.9514790517935283e+20
>>> n - long(float(n))
65535L
```
O resultado de ponto flutuante do Python 2.7 é maior, mas muito mais próximo do valor verdadeiro:
```
>>> n = 295147905179352891391
>>> float(n)
2.9514790517935289e+20
>>> n - long(float(n))
-1L
```
(Implementada por Mark Dickinson; bpo-3166.)

A divisão inteira também é mais precisa em seus comportamentos de arredondamento. (Também implementada por Mark Dickinson; bpo-1811.)
Implicit coercion for complex numbers has been removed; the interpreter will no longer ever attempt to call a __coerce__() method on complex objects. (Removed by Meador Inge and Mark Dickinson; bpo-5211.)
O método str.format() agora tem suporte à numeração automática dos campos de substituição. Isso torna o uso de str.format() mais parecido com o uso da formatação %s:
```
>>> '{}:{}:{}'.format(2009, 04, 'Sunday')
'2009:4:Sunday'
>>> '{}:{}:{day}'.format(2009, 4, day='Sunday')
'2009:4:Sunday'
```
A numeração automática leva os campos da esquerda para a direita, então o primeiro especificador {...} usará o primeiro argumento para str.format(), o próximo especificador usará o próximo argumento e breve. Você não pode misturar a numeração automática e a numeração explícita – numerar todos os seus campos especificadores ou nenhum deles – mas você pode misturar a numeração automática e os campos nomeados, como no segundo exemplo acima. (Contribuição de Eric Smith; bpo-5237.)

Números complexos agora suportam corretamente o uso com format(), e o padrão é alinhamento à direita. A especificação de uma precisão ou separação por vírgula aplica-se às partes reais e imaginárias do número, mas uma largura de campo e alinhamento especificados são aplicados a toda a saída 1.5+3j resultante. (Contribuição de Eric Smith; bpo-1588 e bpo-7988.)

O código de formato ‘F’ agora sempre formata sua saída usando caracteres maiúsculos, então agora produzirá ‘INF’ e ‘NAN’. (Contribuição de Eric Smith; bpo-3382.)

A low-level change: the object.__format__() method now triggers a PendingDeprecationWarning if it’s passed a format string, because the __format__() method for object converts the object to a string representation and formats that. Previously the method silently applied the format string to the string representation, but that could hide mistakes in Python code. If you’re supplying formatting information such as an alignment or precision, presumably you’re expecting the formatting to be applied in some object-specific way. (Fixed by Eric Smith; bpo-7994.)
The int() and long() types gained a bit_length method that returns the number of bits necessary to represent its argument in binary:
```
>>> n = 37
>>> bin(n)
'0b100101'
>>> n.bit_length()
6
>>> n = 2**123-1
>>> n.bit_length()
123
>>> (n+1).bit_length()
124
```
(Contribuição de Fredrik Johansson e Victor Stinner; bpo-3439.)
A instrução import não tentará mais uma importação absoluta se uma importação relativa (por exemplo, from .os import sep) falhar. Isso corrige um bug, mas pode possivelmente quebrar certas instruções import que estavam funcionando apenas por acidente. (Correção de Meador Inge; bpo-7902.)
It’s now possible for a subclass of the built-in unicode type to override the __unicode__() method. (Implemented by Victor Stinner; bpo-1583863.)
O método translate() do tipo bytearray agora aceita None como seu primeiro argumento. (Correção de Georg Brandl; bpo-4759.)
When using @classmethod and @staticmethod to wrap methods as class or static methods, the wrapper object now exposes the wrapped function as their __func__ attribute. (Contributed by Amaury Forgeot d’Arc, after a suggestion by George Sakkis; bpo-5982.)
Quando um conjunto restrito de atributos foi definido usando __slots__, excluir um atributo não definido não levantaria AttributeError como seria de esperar. Correção de Benjamin Peterson; bpo-7604.)
Duas novas codificações agora são suportadas: “cp720”, usado principalmente para texto em árabe; e “cp858”, uma variante do CP 850 que adiciona o símbolo do euro. (CP720 foi contribuição de Alexander Belchenko e Amaury Forgeot d’Arc em bpo-1616979; CP858 foi contribuição de Tim Hatch em bpo-8016.)
The file object will now set the filename attribute on the IOError exception when trying to open a directory on POSIX platforms (noted by Jan Kaliszewski; bpo-4764), and now explicitly checks for and forbids writing to read-only file objects instead of trusting the C library to catch and report the error (fixed by Stefan Krah; bpo-5677).
O tokenizador do Python agora traduz as próprias terminações de linha, então a função embutida compile() agora aceita código usando qualquer convenção de terminação de linha. Além disso, não requer mais que o código termine em uma nova linha.
Parênteses extras em definições de função são ilegais no Python 3.x, o que significa que você obtém um erro de sintaxe de def f((x)): pass. No modo de aviso do Python3, o Python 2.7 agora avisará sobre esse uso estranho. (Notado por James Lingard; bpo-7362.)
Agora é possível criar referências fracas para objetos de classe de estilo antigo. As classes de novo estilo sempre tiveram referências fracas. (Correção de Antoine Pitrou; bpo-8268.)
Quando um objeto de módulo é coletado como lixo, o dicionário do módulo agora só é limpo se ninguém mais estiver mantendo uma referência ao dicionário (bpo-7140).

Alterações do interpretador¶

Uma nova variável de ambiente, PYTHONWARNINGS, permite controlar os avisos. Deve ser definido como uma string contendo configurações de aviso, equivalentes àquelas usadas com a opção -W, separadas por vírgulas. (Contribuição de Brian Curtin; bpo-7301.)

For example, the following setting will print warnings every time they occur, but turn warnings from the Cookie module into an error. (The exact syntax for setting an environment variable varies across operating systems and shells.)

export PYTHONWARNINGS=all,error:::Cookie:0

Otimizações¶

Vários aprimoramentos de desempenho foram adicionados:

A new opcode was added to perform the initial setup for with statements, looking up the __enter__() and __exit__() methods. (Contributed by Benjamin Peterson.)
O coletor de lixo agora funciona melhor para um padrão de uso comum: quando muitos objetos estão sendo alocados sem desalocar nenhum deles. Anteriormente, isso levaria um tempo quadrático para coleta de lixo, mas agora o número de coletas de lixo completas é reduzido à medida que o número de objetos no heap aumenta. A nova lógica só executa uma passagem completa de coleta de lixo quando a geração intermediária tiver sido coletada 10 vezes e quando o número de objetos sobreviventes da geração intermediária exceder 10% do número de objetos da geração mais antiga. (Sugerido por Martin von Löwis e implementado por Antoine Pitrou; bpo-4074.)
O coletor de lixo tenta evitar o rastreamento de contêineres simples que não podem fazer parte de um ciclo. No Python 2.7, isso agora é verdade para tuplas e dicts contendo tipos atômicos (como ints, strings, etc.). Transitivamente, um dict contendo tuplas de tipos atômicos também não será rastreado. Isso ajuda a reduzir o custo de cada coleta de lixo diminuindo o número de objetos a serem considerados e percorridos pelo coletor. (Contribuição de Antoine Pitrou; bpo-4688.)
Inteiros longos agora são armazenados internamente na base 2**15 ou na base 2**30, sendo a base determinada no momento da compilação. Anteriormente, eles eram sempre armazenados na base 2**15. O uso de base 2**30 oferece melhorias significativas de desempenho em máquinas de 64 bits, mas os resultados de benchmark em máquinas de 32 bits foram mistos. Portanto, o padrão é usar base 2**30 em máquinas de 64 bits e base 2**15 em máquinas de 32 bits; no Unix, há uma nova opção de configuração --enable-big-digits que pode ser usada para substituir esse padrão.

Apart from the performance improvements this change should be invisible to end users, with one exception: for testing and debugging purposes there’s a new structseq sys.long_info that provides information about the internal format, giving the number of bits per digit and the size in bytes of the C type used to store each digit:
```
>>> import sys
>>> sys.long_info
sys.long_info(bits_per_digit=30, sizeof_digit=4)
```
(Contribuição de Mark Dickinson; bpo-4258.)

Outro conjunto de alterações tornou os objetos longos alguns bytes menores: 2 bytes menores em sistemas de 32 bits e 6 bytes em sistemas de 64 bits. (Contribuição de Mark Dickinson; bpo-5260.)
O algoritmo de divisão para números inteiros longos ficou mais rápido apertando o loop interno, fazendo deslocamentos em vez de multiplicações e corrigindo uma iteração extra desnecessária. Vários benchmarks mostram acelerações entre 50% e 150% para divisões inteiras longas e operações de módulo. (Contribuição de Mark Dickinson; bpo-5512.) Operações bit a bit também são significativamente mais rápidas (patch inicial de Gregory Smith; bpo-1087418).
A implementação de % verifica se o operando do lado esquerdo é uma string Python e usa casos especiais; isso resulta em um aumento de desempenho de 1 a 3% para aplicativos que usam frequentemente % com strings, como bibliotecas de modelos. (Implementação de Collin Winter; bpo-5176.)
Compreensões de lista com uma condição if são compiladas em bytecode mais rápido. (Patch de Antoine Pitrou, retroportado para 2.7 por Jeffrey Yasskin; bpo-4715.)
A conversão de um inteiro ou inteiro longo em uma string decimal ficou mais rápida com o uso de maiúsculas e minúsculas especiais na base 10, em vez de usar uma função de conversão generalizada que oferece suporte a bases arbitrárias. (Patch por Gawain Bolton; bpo-6713.)
The split(), replace(), rindex(), rpartition(), and rsplit() methods of string-like types (strings, Unicode strings, and bytearray objects) now use a fast reverse-search algorithm instead of a character-by-character scan. This is sometimes faster by a factor of 10. (Added by Florent Xicluna; bpo-7462 and bpo-7622.)
The pickle and cPickle modules now automatically intern the strings used for attribute names, reducing memory usage of the objects resulting from unpickling. (Contributed by Jake McGuire; bpo-5084.)
The cPickle module now special-cases dictionaries, nearly halving the time required to pickle them. (Contributed by Collin Winter; bpo-5670.)

Módulos Novos ou Aprimorados¶

As in every release, Python’s standard library received a number of enhancements and bug fixes. Here’s a partial list of the most notable changes, sorted alphabetically by module name. Consult the Misc/NEWS file in the source tree for a more complete list of changes, or look through the Subversion logs for all the details.

The bdb module’s base debugging class Bdb gained a feature for skipping modules. The constructor now takes an iterable containing glob-style patterns such as django.*; the debugger will not step into stack frames from a module that matches one of these patterns. (Contributed by Maru Newby after a suggestion by Senthil Kumaran; bpo-5142.)
The binascii module now supports the buffer API, so it can be used with memoryview instances and other similar buffer objects. (Backported from 3.x by Florent Xicluna; bpo-7703.)
Updated module: the bsddb module has been updated from 4.7.2devel9 to version 4.8.4 of the pybsddb package. The new version features better Python 3.x compatibility, various bug fixes, and adds several new BerkeleyDB flags and methods. (Updated by Jesús Cea Avión; bpo-8156. The pybsddb changelog can be read at https://hg.jcea.es/pybsddb/file/tip/ChangeLog.)
The bz2 module’s BZ2File now supports the context management protocol, so you can write with bz2.BZ2File(...) as f:. (Contributed by Hagen Fürstenau; bpo-3860.)
New class: the Counter class in the collections module is useful for tallying data. Counter instances behave mostly like dictionaries but return zero for missing keys instead of raising a KeyError:
```
>>> from collections import Counter
>>> c = Counter()
>>> for letter in 'here is a sample of english text':
...   c[letter] += 1
...
>>> c 
Counter({' ': 6, 'e': 5, 's': 3, 'a': 2, 'i': 2, 'h': 2,
'l': 2, 't': 2, 'g': 1, 'f': 1, 'm': 1, 'o': 1, 'n': 1,
'p': 1, 'r': 1, 'x': 1})
>>> c['e']
5
>>> c['z']
0
```
There are three additional Counter methods. most_common() returns the N most common elements and their counts. elements() returns an iterator over the contained elements, repeating each element as many times as its count. subtract() takes an iterable and subtracts one for each element instead of adding; if the argument is a dictionary or another Counter, the counts are subtracted.
```
>>> c.most_common(5)
[(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)]
>>> c.elements() ->
   'a', 'a', ' ', ' ', ' ', ' ', ' ', ' ',
   'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i',
   'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's',
   's', 's', 'r', 't', 't', 'x'
>>> c['e']
5
>>> c.subtract('very heavy on the letter e')
>>> c['e']    # Count is now lower
-1
```
Contributed by Raymond Hettinger; bpo-1696199.

New class: OrderedDict is described in the earlier section PEP 372: Adicionando um dicionário ordenado a coleções.

New method: The deque data type now has a count() method that returns the number of contained elements equal to the supplied argument x, and a reverse() method that reverses the elements of the deque in-place. deque also exposes its maximum length as the read-only maxlen attribute. (Both features added by Raymond Hettinger.)

The namedtuple class now has an optional rename parameter. If rename is true, field names that are invalid because they’ve been repeated or aren’t legal Python identifiers will be renamed to legal names that are derived from the field’s position within the list of fields:
```
>>> from collections import namedtuple
>>> T = namedtuple('T', ['field1', '$illegal', 'for', 'field2'], rename=True)
>>> T._fields
('field1', '_1', '_2', 'field2')
```
(Added by Raymond Hettinger; bpo-1818.)

Finally, the Mapping abstract base class now returns NotImplemented if a mapping is compared to another type that isn’t a Mapping. (Fixed by Daniel Stutzbach; bpo-8729.)

Constructors for the parsing classes in the ConfigParser module now take an allow_no_value parameter, defaulting to false; if true, options without values will be allowed. For example:

>>> import ConfigParser, StringIO
>>> sample_config = """
... [mysqld]
... user = mysql
... pid-file = /var/run/mysqld/mysqld.pid
... skip-bdb
... """
>>> config = ConfigParser.RawConfigParser(allow_no_value=True)
>>> config.readfp(StringIO.StringIO(sample_config))
>>> config.get('mysqld', 'user')
'mysql'
>>> print config.get('mysqld', 'skip-bdb')
None
>>> print config.get('mysqld', 'unknown')
Traceback (most recent call last):
  ...
NoOptionError: No option 'unknown' in section: 'mysqld'

(Contributed by Mats Kindahl; bpo-7005.)

Deprecated function: contextlib.nested(), which allows handling more than one context manager with a single with statement, has been deprecated, because the with statement now supports multiple context managers.
The cookielib module now ignores cookies that have an invalid version field, one that doesn’t contain an integer value. (Fixed by John J. Lee; bpo-3924.)
The copy module’s deepcopy() function will now correctly copy bound instance methods. (Implemented by Robert Collins; bpo-1515.)
The ctypes module now always converts None to a C NULL pointer for arguments declared as pointers. (Changed by Thomas Heller; bpo-4606.) The underlying libffi library has been updated to version 3.0.9, containing various fixes for different platforms. (Updated by Matthias Klose; bpo-8142.)
New method: the datetime module’s timedelta class gained a total_seconds() method that returns the number of seconds in the duration. (Contributed by Brian Quinlan; bpo-5788.)
New method: the Decimal class gained a from_float() class method that performs an exact conversion of a floating-point number to a Decimal. This exact conversion strives for the closest decimal approximation to the floating-point representation’s value; the resulting decimal value will therefore still include the inaccuracy, if any. For example, Decimal.from_float(0.1) returns Decimal('0.1000000000000000055511151231257827021181583404541015625'). (Implemented by Raymond Hettinger; bpo-4796.)

Comparing instances of Decimal with floating-point numbers now produces sensible results based on the numeric values of the operands. Previously such comparisons would fall back to Python’s default rules for comparing objects, which produced arbitrary results based on their type. Note that you still cannot combine Decimal and floating-point in other operations such as addition, since you should be explicitly choosing how to convert between float and Decimal. (Fixed by Mark Dickinson; bpo-2531.)

The constructor for Decimal now accepts floating-point numbers (added by Raymond Hettinger; bpo-8257) and non-European Unicode characters such as Arabic-Indic digits (contributed by Mark Dickinson; bpo-6595).

Most of the methods of the Context class now accept integers as well as Decimal instances; the only exceptions are the canonical() and is_canonical() methods. (Patch by Juan José Conti; bpo-7633.)

When using Decimal instances with a string’s format() method, the default alignment was previously left-alignment. This has been changed to right-alignment, which is more sensible for numeric types. (Changed by Mark Dickinson; bpo-6857.)

Comparisons involving a signaling NaN value (or sNAN) now signal InvalidOperation instead of silently returning a true or false value depending on the comparison operator. Quiet NaN values (or NaN) are now hashable. (Fixed by Mark Dickinson; bpo-7279.)
The difflib module now produces output that is more compatible with modern diff/patch tools through one small change, using a tab character instead of spaces as a separator in the header giving the filename. (Fixed by Anatoly Techtonik; bpo-7585.)
The Distutils sdist command now always regenerates the MANIFEST file, since even if the MANIFEST.in or setup.py files haven’t been modified, the user might have created some new files that should be included. (Fixed by Tarek Ziadé; bpo-8688.)
The doctest module’s IGNORE_EXCEPTION_DETAIL flag will now ignore the name of the module containing the exception being tested. (Patch by Lennart Regebro; bpo-7490.)
The email module’s Message class will now accept a Unicode-valued payload, automatically converting the payload to the encoding specified by output_charset. (Added by R. David Murray; bpo-1368247.)
The Fraction class now accepts a single float or Decimal instance, or two rational numbers, as arguments to its constructor. (Implemented by Mark Dickinson; rationals added in bpo-5812, and float/decimal in bpo-8294.)

Ordering comparisons (<, <=, >, >=) between fractions and complex numbers now raise a TypeError. This fixes an oversight, making the Fraction match the other numeric types.
New class: FTP_TLS in the ftplib module provides secure FTP connections using TLS encapsulation of authentication as well as subsequent control and data transfers. (Contributed by Giampaolo Rodola; bpo-2054.)

The storbinary() method for binary uploads can now restart uploads thanks to an added rest parameter (patch by Pablo Mouzo; bpo-6845.)
New class decorator: total_ordering() in the functools module takes a class that defines an __eq__() method and one of __lt__(), __le__(), __gt__(), or __ge__(), and generates the missing comparison methods. Since the __cmp__() method is being deprecated in Python 3.x, this decorator makes it easier to define ordered classes. (Added by Raymond Hettinger; bpo-5479.)

New function: cmp_to_key() will take an old-style comparison function that expects two arguments and return a new callable that can be used as the key parameter to functions such as sorted(), min() and max(), etc. The primary intended use is to help with making code compatible with Python 3.x. (Added by Raymond Hettinger.)
New function: the gc module’s is_tracked() returns true if a given instance is tracked by the garbage collector, false otherwise. (Contributed by Antoine Pitrou; bpo-4688.)
The gzip module’s GzipFile now supports the context management protocol, so you can write with gzip.GzipFile(...) as f: (contributed by Hagen Fürstenau; bpo-3860), and it now implements the io.BufferedIOBase ABC, so you can wrap it with io.BufferedReader for faster processing (contributed by Nir Aides; bpo-7471). It’s also now possible to override the modification time recorded in a gzipped file by providing an optional timestamp to the constructor. (Contributed by Jacques Frechet; bpo-4272.)

Files in gzip format can be padded with trailing zero bytes; the gzip module will now consume these trailing bytes. (Fixed by Tadek Pietraszek and Brian Curtin; bpo-2846.)
New attribute: the hashlib module now has an algorithms attribute containing a tuple naming the supported algorithms. In Python 2.7, hashlib.algorithms contains ('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512'). (Contributed by Carl Chenet; bpo-7418.)
The default HTTPResponse class used by the httplib module now supports buffering, resulting in much faster reading of HTTP responses. (Contributed by Kristján Valur Jónsson; bpo-4879.)

The HTTPConnection and HTTPSConnection classes now support a source_address parameter, a (host, port) 2-tuple giving the source address that will be used for the connection. (Contributed by Eldon Ziegler; bpo-3972.)
The ihooks module now supports relative imports. Note that ihooks is an older module for customizing imports, superseded by the imputil module added in Python 2.0. (Relative import support added by Neil Schemenauer.)
The imaplib module now supports IPv6 addresses. (Contributed by Derek Morr; bpo-1655.)

New function: the inspect module’s getcallargs() takes a callable and its positional and keyword arguments, and figures out which of the callable’s parameters will receive each argument, returning a dictionary mapping argument names to their values. For example:

>>> from inspect import getcallargs
>>> def f(a, b=1, *pos, **named):
...     pass
...
>>> getcallargs(f, 1, 2, 3)
{'a': 1, 'b': 2, 'pos': (3,), 'named': {}}
>>> getcallargs(f, a=2, x=4)
{'a': 2, 'b': 1, 'pos': (), 'named': {'x': 4}}
>>> getcallargs(f)
Traceback (most recent call last):
...
TypeError: f() takes at least 1 argument (0 given)

Contributed by George Sakkis; bpo-3135.

Updated module: The io library has been upgraded to the version shipped with Python 3.1. For 3.1, the I/O library was entirely rewritten in C and is 2 to 20 times faster depending on the task being performed. The original Python version was renamed to the _pyio module.

One minor resulting change: the io.TextIOBase class now has an errors attribute giving the error setting used for encoding and decoding errors (one of 'strict', 'replace', 'ignore').

The io.FileIO class now raises an OSError when passed an invalid file descriptor. (Implemented by Benjamin Peterson; bpo-4991.) The truncate() method now preserves the file position; previously it would change the file position to the end of the new file. (Fixed by Pascal Chambon; bpo-6939.)
New function: itertools.compress(data, selectors) takes two iterators. Elements of data are returned if the corresponding value in selectors is true:
```
itertools.compress('ABCDEF', [1,0,1,0,1,1]) =>
  A, C, E, F
```
New function: itertools.combinations_with_replacement(iter, r) returns all the possible r-length combinations of elements from the iterable iter. Unlike combinations(), individual elements can be repeated in the generated combinations:
```
itertools.combinations_with_replacement('abc', 2) =>
  ('a', 'a'), ('a', 'b'), ('a', 'c'),
  ('b', 'b'), ('b', 'c'), ('c', 'c')
```
Note that elements are treated as unique depending on their position in the input, not their actual values.

The itertools.count() function now has a step argument that allows incrementing by values other than 1. count() also now allows keyword arguments, and using non-integer values such as floats or Decimal instances. (Implemented by Raymond Hettinger; bpo-5032.)

itertools.combinations() and itertools.product() previously raised ValueError for values of r larger than the input iterable. This was deemed a specification error, so they now return an empty iterator. (Fixed by Raymond Hettinger; bpo-4816.)
Updated module: The json module was upgraded to version 2.0.9 of the simplejson package, which includes a C extension that makes encoding and decoding faster. (Contributed by Bob Ippolito; bpo-4136.)

To support the new collections.OrderedDict type, json.load() now has an optional object_pairs_hook parameter that will be called with any object literal that decodes to a list of pairs. (Contributed by Raymond Hettinger; bpo-5381.)
The mailbox module’s Maildir class now records the timestamp on the directories it reads, and only re-reads them if the modification time has subsequently changed. This improves performance by avoiding unneeded directory scans. (Fixed by A.M. Kuchling and Antoine Pitrou; bpo-1607951, bpo-6896.)
New functions: the math module gained erf() and erfc() for the error function and the complementary error function, expm1() which computes e**x - 1 with more precision than using exp() and subtracting 1, gamma() for the Gamma function, and lgamma() for the natural log of the Gamma function. (Contributed by Mark Dickinson and nirinA raseliarison; bpo-3366.)
The multiprocessing module’s Manager* classes can now be passed a callable that will be called whenever a subprocess is started, along with a set of arguments that will be passed to the callable. (Contributed by lekma; bpo-5585.)

The Pool class, which controls a pool of worker processes, now has an optional maxtasksperchild parameter. Worker processes will perform the specified number of tasks and then exit, causing the Pool to start a new worker. This is useful if tasks may leak memory or other resources, or if some tasks will cause the worker to become very large. (Contributed by Charles Cazabon; bpo-6963.)
The nntplib module now supports IPv6 addresses. (Contributed by Derek Morr; bpo-1664.)
New functions: the os module wraps the following POSIX system calls: getresgid() and getresuid(), which return the real, effective, and saved GIDs and UIDs; setresgid() and setresuid(), which set real, effective, and saved GIDs and UIDs to new values; initgroups(), which initialize the group access list for the current process. (GID/UID functions contributed by Travis H.; bpo-6508. Support for initgroups added by Jean-Paul Calderone; bpo-7333.)

The os.fork() function now re-initializes the import lock in the child process; this fixes problems on Solaris when fork() is called from a thread. (Fixed by Zsolt Cserna; bpo-7242.)
In the os.path module, the normpath() and abspath() functions now preserve Unicode; if their input path is a Unicode string, the return value is also a Unicode string. (normpath() fixed by Matt Giuca in bpo-5827; abspath() fixed by Ezio Melotti in bpo-3426.)
The pydoc module now has help for the various symbols that Python uses. You can now do help('<<') or help('@'), for example. (Contributed by David Laban; bpo-4739.)
The re module’s split(), sub(), and subn() now accept an optional flags argument, for consistency with the other functions in the module. (Added by Gregory P. Smith.)
New function: run_path() in the runpy module will execute the code at a provided path argument. path can be the path of a Python source file (example.py), a compiled bytecode file (example.pyc), a directory (./package/), or a zip archive (example.zip). If a directory or zip path is provided, it will be added to the front of sys.path and the module __main__ will be imported. It’s expected that the directory or zip contains a __main__.py; if it doesn’t, some other __main__.py might be imported from a location later in sys.path. This makes more of the machinery of runpy available to scripts that want to mimic the way Python’s command line processes an explicit path name. (Added by Nick Coghlan; bpo-6816.)
New function: in the shutil module, make_archive() takes a filename, archive type (zip or tar-format), and a directory path, and creates an archive containing the directory’s contents. (Added by Tarek Ziadé.)

shutil’s copyfile() and copytree() functions now raise a SpecialFileError exception when asked to copy a named pipe. Previously the code would treat named pipes like a regular file by opening them for reading, and this would block indefinitely. (Fixed by Antoine Pitrou; bpo-3002.)
The signal module no longer re-installs the signal handler unless this is truly necessary, which fixes a bug that could make it impossible to catch the EINTR signal robustly. (Fixed by Charles-Francois Natali; bpo-8354.)
New functions: in the site module, three new functions return various site- and user-specific paths. getsitepackages() returns a list containing all global site-packages directories, getusersitepackages() returns the path of the user’s site-packages directory, and getuserbase() returns the value of the USER_BASE environment variable, giving the path to a directory that can be used to store data. (Contributed by Tarek Ziadé; bpo-6693.)

The site module now reports exceptions occurring when the sitecustomize module is imported, and will no longer catch and swallow the KeyboardInterrupt exception. (Fixed by Victor Stinner; bpo-3137.)
The create_connection() function gained a source_address parameter, a (host, port) 2-tuple giving the source address that will be used for the connection. (Contributed by Eldon Ziegler; bpo-3972.)

The recv_into() and recvfrom_into() methods will now write into objects that support the buffer API, most usefully the bytearray and memoryview objects. (Implemented by Antoine Pitrou; bpo-8104.)
The SocketServer module’s TCPServer class now supports socket timeouts and disabling the Nagle algorithm. The disable_nagle_algorithm class attribute defaults to False; if overridden to be true, new request connections will have the TCP_NODELAY option set to prevent buffering many small sends into a single TCP packet. The timeout class attribute can hold a timeout in seconds that will be applied to the request socket; if no request is received within that time, handle_timeout() will be called and handle_request() will return. (Contributed by Kristján Valur Jónsson; bpo-6192 and bpo-6267.)
Updated module: the sqlite3 module has been updated to version 2.6.0 of the pysqlite package. Version 2.6.0 includes a number of bugfixes, and adds the ability to load SQLite extensions from shared libraries. Call the enable_load_extension(True) method to enable extensions, and then call load_extension() to load a particular shared library. (Updated by Gerhard Häring.)
The ssl module’s SSLSocket objects now support the buffer API, which fixed a test suite failure (fix by Antoine Pitrou; bpo-7133) and automatically set OpenSSL’s SSL_MODE_AUTO_RETRY, which will prevent an error code being returned from recv() operations that trigger an SSL renegotiation (fix by Antoine Pitrou; bpo-8222).

The wrap_socket() constructor function now takes a ciphers argument that’s a string listing the encryption algorithms to be allowed; the format of the string is described in the OpenSSL documentation. (Added by Antoine Pitrou; bpo-8322.)

Another change makes the extension load all of OpenSSL’s ciphers and digest algorithms so that they’re all available. Some SSL certificates couldn’t be verified, reporting an “unknown algorithm” error. (Reported by Beda Kosata, and fixed by Antoine Pitrou; bpo-8484.)

The version of OpenSSL being used is now available as the module attributes ssl.OPENSSL_VERSION (a string), ssl.OPENSSL_VERSION_INFO (a 5-tuple), and ssl.OPENSSL_VERSION_NUMBER (an integer). (Added by Antoine Pitrou; bpo-8321.)
The struct module will no longer silently ignore overflow errors when a value is too large for a particular integer format code (one of bBhHiIlLqQ); it now always raises a struct.error exception. (Changed by Mark Dickinson; bpo-1523.) The pack() function will also attempt to use __index__() to convert and pack non-integers before trying the __int__() method or reporting an error. (Changed by Mark Dickinson; bpo-8300.)
New function: the subprocess module’s check_output() runs a command with a specified set of arguments and returns the command’s output as a string when the command runs without error, or raises a CalledProcessError exception otherwise.
```
>>> subprocess.check_output(['df', '-h', '.'])
'Filesystem     Size   Used  Avail Capacity  Mounted on\n
/dev/disk0s2    52G    49G   3.0G    94%    /\n'

>>> subprocess.check_output(['df', '-h', '/bogus'])
  ...
subprocess.CalledProcessError: Command '['df', '-h', '/bogus']' returned non-zero exit status 1
```
(Contributed by Gregory P. Smith.)

The subprocess module will now retry its internal system calls on receiving an EINTR signal. (Reported by several people; final patch by Gregory P. Smith in bpo-1068268.)
New function: is_declared_global() in the symtable module returns true for variables that are explicitly declared to be global, false for ones that are implicitly global. (Contributed by Jeremy Hylton.)
The syslog module will now use the value of sys.argv[0] as the identifier instead of the previous default value of 'python'. (Changed by Sean Reifschneider; bpo-8451.)
The sys.version_info value is now a named tuple, with attributes named major, minor, micro, releaselevel, and serial. (Contributed by Ross Light; bpo-4285.)

sys.getwindowsversion() also returns a named tuple, with attributes named major, minor, build, platform, service_pack, service_pack_major, service_pack_minor, suite_mask, and product_type. (Contributed by Brian Curtin; bpo-7766.)
The tarfile module’s default error handling has changed, to no longer suppress fatal errors. The default error level was previously 0, which meant that errors would only result in a message being written to the debug log, but because the debug log is not activated by default, these errors go unnoticed. The default error level is now 1, which raises an exception if there’s an error. (Changed by Lars Gustäbel; bpo-7357.)

tarfile now supports filtering the TarInfo objects being added to a tar file. When you call add(), you may supply an optional filter argument that’s a callable. The filter callable will be passed the TarInfo for every file being added, and can modify and return it. If the callable returns None, the file will be excluded from the resulting archive. This is more powerful than the existing exclude argument, which has therefore been deprecated. (Added by Lars Gustäbel; bpo-6856.) The TarFile class also now supports the context management protocol. (Added by Lars Gustäbel; bpo-7232.)
The wait() method of the threading.Event class now returns the internal flag on exit. This means the method will usually return true because wait() is supposed to block until the internal flag becomes true. The return value will only be false if a timeout was provided and the operation timed out. (Contributed by Tim Lesher; bpo-1674032.)
The Unicode database provided by the unicodedata module is now used internally to determine which characters are numeric, whitespace, or represent line breaks. The database also includes information from the Unihan.txt data file (patch by Anders Chrigström and Amaury Forgeot d’Arc; bpo-1571184) and has been updated to version 5.2.0 (updated by Florent Xicluna; bpo-8024).
The urlparse module’s urlsplit() now handles unknown URL schemes in a fashion compliant with RFC 3986: if the URL is of the form "<something>://...", the text before the :// is treated as the scheme, even if it’s a made-up scheme that the module doesn’t know about. This change may break code that worked around the old behaviour. For example, Python 2.6.4 or 2.5 will return the following:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', '', '//host/filename?query', '', '')
```
Python 2.7 (and Python 2.6.5) will return:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', 'host', '/filename?query', '', '')
```
(Python 2.7 actually produces slightly different output, since it returns a named tuple instead of a standard tuple.)

The urlparse module also supports IPv6 literal addresses as defined by RFC 2732 (contributed by Senthil Kumaran; bpo-2987).
```
>>> urlparse.urlparse('http://[1080::8:800:200C:417A]/foo')
ParseResult(scheme='http', netloc='[1080::8:800:200C:417A]',
            path='/foo', params='', query='', fragment='')
```
New class: the WeakSet class in the weakref module is a set that only holds weak references to its elements; elements will be removed once there are no references pointing to them. (Originally implemented in Python 3.x by Raymond Hettinger, and backported to 2.7 by Michael Foord.)
The xml.etree.ElementTree library, no longer escapes ampersands and angle brackets when outputting an XML processing instruction (which looks like <?xml-stylesheet href="#style1"?>) or comment (which looks like ). (Patch by Neil Muller; bpo-2746.)
The XML-RPC client and server, provided by the xmlrpclib and SimpleXMLRPCServer modules, have improved performance by supporting HTTP/1.1 keep-alive and by optionally using gzip encoding to compress the XML being exchanged. The gzip compression is controlled by the encode_threshold attribute of SimpleXMLRPCRequestHandler, which contains a size in bytes; responses larger than this will be compressed. (Contributed by Kristján Valur Jónsson; bpo-6267.)
The zipfile module’s ZipFile now supports the context management protocol, so you can write with zipfile.ZipFile(...) as f:. (Contributed by Brian Curtin; bpo-5511.)

zipfile now also supports archiving empty directories and extracts them correctly. (Fixed by Kuba Wieczorek; bpo-4710.) Reading files out of an archive is faster, and interleaving read() and readline() now works correctly. (Contributed by Nir Aides; bpo-7610.)

The is_zipfile() function now accepts a file object, in addition to the path names accepted in earlier versions. (Contributed by Gabriel Genellina; bpo-4756.)

The writestr() method now has an optional compress_type parameter that lets you override the default compression method specified in the ZipFile constructor. (Contributed by Ronald Oussoren; bpo-6003.)

New module: importlib¶

Python 3.1 includes the importlib package, a re-implementation of the logic underlying Python’s import statement. importlib is useful for implementors of Python interpreters and to users who wish to write new importers that can participate in the import process. Python 2.7 doesn’t contain the complete importlib package, but instead has a tiny subset that contains a single function, import_module().

import_module(name, package=None) imports a module. name is a string containing the module or package’s name. It’s possible to do relative imports by providing a string that begins with a . character, such as ..utils.errors. For relative imports, the package argument must be provided and is the name of the package that will be used as the anchor for the relative import. import_module() both inserts the imported module into sys.modules and returns the module object.

Here are some examples:

>>> from importlib import import_module
>>> anydbm = import_module('anydbm')  # Standard absolute import
>>> anydbm
<module 'anydbm' from '/p/python/Lib/anydbm.py'>
>>> # Relative import
>>> file_util = import_module('..file_util', 'distutils.command')
>>> file_util
<module 'distutils.file_util' from '/python/Lib/distutils/file_util.pyc'>

importlib was implemented by Brett Cannon and introduced in Python 3.1.

New module: sysconfig¶

The sysconfig module has been pulled out of the Distutils package, becoming a new top-level module in its own right. sysconfig provides functions for getting information about Python’s build process: compiler switches, installation paths, the platform name, and whether Python is running from its source directory.

Some of the functions in the module are:

get_config_var() returns variables from Python’s Makefile and the pyconfig.h file.
get_config_vars() returns a dictionary containing all of the configuration variables.
get_path() returns the configured path for a particular type of module: the standard library, site-specific modules, platform-specific modules, etc.
is_python_build() returns true if you’re running a binary from a Python source tree, and false otherwise.

Consult the sysconfig documentation for more details and for a complete list of functions.

The Distutils package and sysconfig are now maintained by Tarek Ziadé, who has also started a Distutils2 package (source repository at https://hg.python.org/distutils2/) for developing a next-generation version of Distutils.

ttk: Themed Widgets for Tk¶

Tcl/Tk 8.5 includes a set of themed widgets that re-implement basic Tk widgets but have a more customizable appearance and can therefore more closely resemble the native platform’s widgets. This widget set was originally called Tile, but was renamed to Ttk (for “themed Tk”) on being added to Tcl/Tck release 8.5.

To learn more, read the ttk module documentation. You may also wish to read the Tcl/Tk manual page describing the Ttk theme engine, available at https://www.tcl.tk/man/tcl8.5/TkCmd/ttk_intro.html. Some screenshots of the Python/Ttk code in use are at https://code.google.com/archive/p/python-ttk/wikis/Screenshots.wiki.

The tkinter.ttk module was written by Guilherme Polo and added in bpo-2983. An alternate version called Tile.py, written by Martin Franklin and maintained by Kevin Walzer, was proposed for inclusion in bpo-2618, but the authors argued that Guilherme Polo’s work was more comprehensive.

Updated module: unittest¶

The unittest module was greatly enhanced; many new features were added. Most of these features were implemented by Michael Foord, unless otherwise noted. The enhanced version of the module is downloadable separately for use with Python versions 2.4 to 2.6, packaged as the unittest2 package, from unittest2.

When used from the command line, the module can automatically discover tests. It’s not as fancy as py.test or nose, but provides a simple way to run tests kept within a set of package directories. For example, the following command will search the test/ subdirectory for any importable test files named test*.py:

python -m unittest discover -s test

Consult the unittest module documentation for more details. (Developed in bpo-6001.)

The main() function supports some other new options:

-b or --buffer will buffer the standard output and standard error streams during each test. If the test passes, any resulting output will be discarded; on failure, the buffered output will be displayed.
-c or --catch will cause the control-C interrupt to be handled more gracefully. Instead of interrupting the test process immediately, the currently running test will be completed and then the partial results up to the interruption will be reported. If you’re impatient, a second press of control-C will cause an immediate interruption.

This control-C handler tries to avoid causing problems when the code being tested or the tests being run have defined a signal handler of their own, by noticing that a signal handler was already set and calling it. If this doesn’t work for you, there’s a removeHandler() decorator that can be used to mark tests that should have the control-C handling disabled.
-f or --failfast makes test execution stop immediately when a test fails instead of continuing to execute further tests. (Suggested by Cliff Dyer and implemented by Michael Foord; bpo-8074.)

The progress messages now show ‘x’ for expected failures and ‘u’ for unexpected successes when run in verbose mode. (Contributed by Benjamin Peterson.)

Test cases can raise the SkipTest exception to skip a test (bpo-1034053).

The error messages for assertEqual(), assertTrue(), and assertFalse() failures now provide more information. If you set the longMessage attribute of your TestCase classes to true, both the standard error message and any additional message you provide will be printed for failures. (Added by Michael Foord; bpo-5663.)

The assertRaises() method now returns a context handler when called without providing a callable object to run. For example, you can write this:

with self.assertRaises(KeyError):
    {}['foo']

(Implemented by Antoine Pitrou; bpo-4444.)

Module- and class-level setup and teardown fixtures are now supported. Modules can contain setUpModule() and tearDownModule() functions. Classes can have setUpClass() and tearDownClass() methods that must be defined as class methods (using @classmethod or equivalent). These functions and methods are invoked when the test runner switches to a test case in a different module or class.

The methods addCleanup() and doCleanups() were added. addCleanup() lets you add cleanup functions that will be called unconditionally (after setUp() if setUp() fails, otherwise after tearDown()). This allows for much simpler resource allocation and deallocation during tests (bpo-5679).

A number of new methods were added that provide more specialized tests. Many of these methods were written by Google engineers for use in their test suites; Gregory P. Smith, Michael Foord, and GvR worked on merging them into Python’s version of unittest.

assertIsNone() and assertIsNotNone() take one expression and verify that the result is or is not None.
assertIs() and assertIsNot() take two values and check whether the two values evaluate to the same object or not. (Added by Michael Foord; bpo-2578.)
assertIsInstance() and assertNotIsInstance() check whether the resulting object is an instance of a particular class, or of one of a tuple of classes. (Added by Georg Brandl; bpo-7031.)
assertGreater(), assertGreaterEqual(), assertLess(), and assertLessEqual() compare two quantities.
assertMultiLineEqual() compares two strings, and if they’re not equal, displays a helpful comparison that highlights the differences in the two strings. This comparison is now used by default when Unicode strings are compared with assertEqual().
assertRegexpMatches() and assertNotRegexpMatches() checks whether the first argument is a string matching or not matching the regular expression provided as the second argument (bpo-8038).
assertRaisesRegexp() checks whether a particular exception is raised, and then also checks that the string representation of the exception matches the provided regular expression.
assertIn() and assertNotIn() tests whether first is or is not in second.
assertItemsEqual() tests whether two provided sequences contain the same elements.
assertSetEqual() compares whether two sets are equal, and only reports the differences between the sets in case of error.
Similarly, assertListEqual() and assertTupleEqual() compare the specified types and explain any differences without necessarily printing their full values; these methods are now used by default when comparing lists and tuples using assertEqual(). More generally, assertSequenceEqual() compares two sequences and can optionally check whether both sequences are of a particular type.
assertDictEqual() compares two dictionaries and reports the differences; it’s now used by default when you compare two dictionaries using assertEqual(). assertDictContainsSubset() checks whether all of the key/value pairs in first are found in second.
assertAlmostEqual() and assertNotAlmostEqual() test whether first and second are approximately equal. This method can either round their difference to an optionally specified number of places (the default is 7) and compare it to zero, or require the difference to be smaller than a supplied delta value.
loadTestsFromName() properly honors the suiteClass attribute of the TestLoader. (Fixed by Mark Roddy; bpo-6866.)
A new hook lets you extend the assertEqual() method to handle new data types. The addTypeEqualityFunc() method takes a type object and a function. The function will be used when both of the objects being compared are of the specified type. This function should compare the two objects and raise an exception if they don’t match; it’s a good idea for the function to provide additional information about why the two objects aren’t matching, much as the new sequence comparison methods do.

unittest.main() now takes an optional exit argument. If false, main() doesn’t call sys.exit(), allowing main() to be used from the interactive interpreter. (Contributed by J. Pablo Fernández; bpo-3379.)

TestResult has new startTestRun() and stopTestRun() methods that are called immediately before and after a test run. (Contributed by Robert Collins; bpo-5728.)

With all these changes, the unittest.py was becoming awkwardly large, so the module was turned into a package and the code split into several files (by Benjamin Peterson). This doesn’t affect how the module is imported or used.

Ver também

https://web.archive.org/web/20210619163128/http://www.voidspace.org.uk/python/articles/unittest2.shtml: Describes the new features, how to use them, and the rationale for various design decisions. (By Michael Foord.)

Updated module: ElementTree 1.3¶

The version of the ElementTree library included with Python was updated to version 1.3. Some of the new features are:

The various parsing functions now take a parser keyword argument giving an XMLParser instance that will be used. This makes it possible to override the file’s internal encoding:
```
p = ET.XMLParser(encoding='utf-8')
t = ET.XML("""<root/>""", parser=p)
```
Errors in parsing XML now raise a ParseError exception, whose instances have a position attribute containing a (line, column) tuple giving the location of the problem.
ElementTree’s code for converting trees to a string has been significantly reworked, making it roughly twice as fast in many cases. The ElementTree.write() and Element.write() methods now have a method parameter that can be “xml” (the default), “html”, or “text”. HTML mode will output empty elements as <empty></empty> instead of <empty/>, and text mode will skip over elements and only output the text chunks. If you set the tag attribute of an element to None but leave its children in place, the element will be omitted when the tree is written out, so you don’t need to do more extensive rearrangement to remove a single element.

Namespace handling has also been improved. All xmlns:<whatever> declarations are now output on the root element, not scattered throughout the resulting XML. You can set the default namespace for a tree by setting the default_namespace attribute and can register new prefixes with register_namespace(). In XML mode, you can use the true/false xml_declaration parameter to suppress the XML declaration.

New Element method: extend() appends the items from a sequence to the element’s children. Elements themselves behave like sequences, so it’s easy to move children from one element to another:

from xml.etree import ElementTree as ET

t = ET.XML("""<list>
  <item>1</item> <item>2</item>  <item>3</item>
</list>""")
new = ET.XML('<root/>')
new.extend(t)

# Outputs <root><item>1</item>...</root>
print ET.tostring(new)

New Element method: iter() yields the children of the element as a generator. It’s also possible to write for child in elem: to loop over an element’s children. The existing method getiterator() is now deprecated, as is getchildren() which constructs and returns a list of children.

New Element method: itertext() yields all chunks of text that are descendants of the element. For example:

t = ET.XML("""<list>
  <item>1</item> <item>2</item>  <item>3</item>
</list>""")

# Outputs ['\n  ', '1', ' ', '2', '  ', '3', '\n']
print list(t.itertext())

Deprecated: using an element as a Boolean (i.e., if elem:) would return true if the element had any children, or false if there were no children. This behaviour is confusing – None is false, but so is a childless element? – so it will now trigger a FutureWarning. In your code, you should be explicit: write len(elem) != 0 if you’re interested in the number of children, or elem is not None.

Fredrik Lundh develops ElementTree and produced the 1.3 version; you can read his article describing 1.3 at https://web.archive.org/web/20200703234532/http://effbot.org/zone/elementtree-13-intro.htm. Florent Xicluna updated the version included with Python, after discussions on python-dev and in bpo-6472.)

Alterações a compilações e API C¶

Changes to Python’s build process and to the C API include:

The latest release of the GNU Debugger, GDB 7, can be scripted using Python. When you begin debugging an executable program P, GDB will look for a file named P-gdb.py and automatically read it. Dave Malcolm contributed a python-gdb.py that adds a number of commands useful when debugging Python itself. For example, py-up and py-down go up or down one Python stack frame, which usually corresponds to several C stack frames. py-print prints the value of a Python variable, and py-bt prints the Python stack trace. (Added as a result of bpo-8032.)
If you use the .gdbinit file provided with Python, the “pyo” macro in the 2.7 version now works correctly when the thread being debugged doesn’t hold the GIL; the macro now acquires it before printing. (Contributed by Victor Stinner; bpo-3632.)
Py_AddPendingCall() is now thread-safe, letting any worker thread submit notifications to the main Python thread. This is particularly useful for asynchronous IO operations. (Contributed by Kristján Valur Jónsson; bpo-4293.)
New function: PyCode_NewEmpty() creates an empty code object; only the filename, function name, and first line number are required. This is useful for extension modules that are attempting to construct a more useful traceback stack. Previously such extensions needed to call PyCode_New(), which had many more arguments. (Added by Jeffrey Yasskin.)
New function: PyErr_NewExceptionWithDoc() creates a new exception class, just as the existing PyErr_NewException() does, but takes an extra char * argument containing the docstring for the new exception class. (Added by ‘lekma’ on the Python bug tracker; bpo-7033.)
New function: PyFrame_GetLineNumber() takes a frame object and returns the line number that the frame is currently executing. Previously code would need to get the index of the bytecode instruction currently executing, and then look up the line number corresponding to that address. (Added by Jeffrey Yasskin.)
New functions: PyLong_AsLongAndOverflow() and PyLong_AsLongLongAndOverflow() approximates a Python long integer as a C long or long long. If the number is too large to fit into the output type, an overflow flag is set and returned to the caller. (Contributed by Case Van Horsen; bpo-7528 and bpo-7767.)
New function: stemming from the rewrite of string-to-float conversion, a new PyOS_string_to_double() function was added. The old PyOS_ascii_strtod() and PyOS_ascii_atof() functions are now deprecated.
New function: PySys_SetArgvEx() sets the value of sys.argv and can optionally update sys.path to include the directory containing the script named by sys.argv[0] depending on the value of an updatepath parameter.

This function was added to close a security hole for applications that embed Python. The old function, PySys_SetArgv(), would always update sys.path, and sometimes it would add the current directory. This meant that, if you ran an application embedding Python in a directory controlled by someone else, attackers could put a Trojan-horse module in the directory (say, a file named os.py) that your application would then import and run.

If you maintain a C/C++ application that embeds Python, check whether you’re calling PySys_SetArgv() and carefully consider whether the application should be using PySys_SetArgvEx() with updatepath set to false.

Security issue reported as CVE-2008-5983; discussed in bpo-5753, and fixed by Antoine Pitrou.
New macros: the Python header files now define the following macros: Py_ISALNUM, Py_ISALPHA, Py_ISDIGIT, Py_ISLOWER, Py_ISSPACE, Py_ISUPPER, Py_ISXDIGIT, Py_TOLOWER, and Py_TOUPPER. All of these functions are analogous to the C standard macros for classifying characters, but ignore the current locale setting, because in several places Python needs to analyze characters in a locale-independent way. (Added by Eric Smith; bpo-5793.)
Removed function: PyEval_CallObject() is now only available as a macro. A function version was being kept around to preserve ABI linking compatibility, but that was in 1997; it can certainly be deleted by now. (Removed by Antoine Pitrou; bpo-8276.)
New format codes: the PyString_FromFormat(), PyString_FromFormatV(), and PyErr_Format() functions now accept %lld and %llu format codes for displaying C’s long long types. (Contributed by Mark Dickinson; bpo-7228.)
The complicated interaction between threads and process forking has been changed. Previously, the child process created by os.fork() might fail because the child is created with only a single thread running, the thread performing the os.fork(). If other threads were holding a lock, such as Python’s import lock, when the fork was performed, the lock would still be marked as “held” in the new process. But in the child process nothing would ever release the lock, since the other threads weren’t replicated, and the child process would no longer be able to perform imports.

Python 2.7 acquires the import lock before performing an os.fork(), and will also clean up any locks created using the threading module. C extension modules that have internal locks, or that call fork() themselves, will not benefit from this clean-up.

(Fixed by Thomas Wouters; bpo-1590864.)
The Py_Finalize() function now calls the internal threading._shutdown() function; this prevents some exceptions from being raised when an interpreter shuts down. (Patch by Adam Olsen; bpo-1722344.)
When using the PyMemberDef structure to define attributes of a type, Python will no longer let you try to delete or set a T_STRING_INPLACE attribute.
Global symbols defined by the ctypes module are now prefixed with Py, or with _ctypes. (Implemented by Thomas Heller; bpo-3102.)
New configure option: the --with-system-expat switch allows building the pyexpat module to use the system Expat library. (Contributed by Arfrever Frehtes Taifersar Arahesis; bpo-7609.)
New configure option: the --with-valgrind option will now disable the pymalloc allocator, which is difficult for the Valgrind memory-error detector to analyze correctly. Valgrind will therefore be better at detecting memory leaks and overruns. (Contributed by James Henstridge; bpo-2422.)
New configure option: you can now supply an empty string to --with-dbmliborder= in order to disable all of the various DBM modules. (Added by Arfrever Frehtes Taifersar Arahesis; bpo-6491.)
The configure script now checks for floating-point rounding bugs on certain 32-bit Intel chips and defines a X87_DOUBLE_ROUNDING preprocessor definition. No code currently uses this definition, but it’s available if anyone wishes to use it. (Added by Mark Dickinson; bpo-2937.)

configure also now sets a LDCXXSHARED Makefile variable for supporting C++ linking. (Contributed by Arfrever Frehtes Taifersar Arahesis; bpo-1222585.)
The build process now creates the necessary files for pkg-config support. (Contributed by Clinton Roy; bpo-3585.)
The build process now supports Subversion 1.7. (Contributed by Arfrever Frehtes Taifersar Arahesis; bpo-6094.)

Capsules¶

Python 3.1 adds a new C datatype, PyCapsule, for providing a C API to an extension module. A capsule is essentially the holder of a C void * pointer, and is made available as a module attribute; for example, the socket module’s API is exposed as socket.CAPI, and unicodedata exposes ucnhash_CAPI. Other extensions can import the module, access its dictionary to get the capsule object, and then get the void * pointer, which will usually point to an array of pointers to the module’s various API functions.

There is an existing data type already used for this, PyCObject, but it doesn’t provide type safety. Evil code written in pure Python could cause a segmentation fault by taking a PyCObject from module A and somehow substituting it for the PyCObject in module B. Capsules know their own name, and getting the pointer requires providing the name:

void *vtable;

if (!PyCapsule_IsValid(capsule, "mymodule.CAPI") {
        PyErr_SetString(PyExc_ValueError, "argument type invalid");
        return NULL;
}

vtable = PyCapsule_GetPointer(capsule, "mymodule.CAPI");

You are assured that vtable points to whatever you’re expecting. If a different capsule was passed in, PyCapsule_IsValid() would detect the mismatched name and return false. Refer to Providing a C API for an Extension Module for more information on using these objects.

Python 2.7 now uses capsules internally to provide various extension-module APIs, but the PyCObject_AsVoidPtr() was modified to handle capsules, preserving compile-time compatibility with the PyCObject interface. Use of PyCObject_AsVoidPtr() will signal a PendingDeprecationWarning, which is silent by default.

Implemented in Python 3.1 and backported to 2.7 by Larry Hastings; discussed in bpo-5630.

Port-Specific Changes: Windows¶

The msvcrt module now contains some constants from the crtassem.h header file: CRT_ASSEMBLY_VERSION, VC_ASSEMBLY_PUBLICKEYTOKEN, and LIBRARIES_ASSEMBLY_NAME_PREFIX. (Contributed by David Cournapeau; bpo-4365.)
The _winreg module for accessing the registry now implements the CreateKeyEx() and DeleteKeyEx() functions, extended versions of previously supported functions that take several extra arguments. The DisableReflectionKey(), EnableReflectionKey(), and QueryReflectionKey() were also tested and documented. (Implemented by Brian Curtin: bpo-7347.)
The new _beginthreadex() API is used to start threads, and the native thread-local storage functions are now used. (Contributed by Kristján Valur Jónsson; bpo-3582.)
The os.kill() function now works on Windows. The signal value can be the constants CTRL_C_EVENT, CTRL_BREAK_EVENT, or any integer. The first two constants will send Control-C and Control-Break keystroke events to subprocesses; any other value will use the TerminateProcess() API. (Contributed by Miki Tebeka; bpo-1220212.)
The os.listdir() function now correctly fails for an empty path. (Fixed by Hirokazu Yamamoto; bpo-5913.)
The mimetypes module will now read the MIME database from the Windows registry when initializing. (Patch by Gabriel Genellina; bpo-4969.)

Port-Specific Changes: Mac OS X¶

The path /Library/Python/2.7/site-packages is now appended to sys.path, in order to share added packages between the system installation and a user-installed copy of the same version. (Changed by Ronald Oussoren; bpo-4865.)

Alterado na versão 2.7.13: As of 2.7.13, this change was removed. /Library/Python/2.7/site-packages, the site-packages directory used by the Apple-supplied system Python 2.7 is no longer appended to sys.path for user-installed Pythons such as from the python.org installers. As of macOS 10.12, Apple changed how the system site-packages directory is configured, which could cause installation of pip components, like setuptools, to fail. Packages installed for the system Python will no longer be shared with user-installed Pythons. (bpo-28440)

Port-Specific Changes: FreeBSD¶

FreeBSD 7.1’s SO_SETFIB constant, used with the socket() methods getsockopt()/setsockopt() to select an alternate routing table, is now available in the socket module. (Added by Kyle VanderBeek; bpo-8235.)

Other Changes and Fixes¶

Two benchmark scripts, iobench and ccbench, were added to the Tools directory. iobench measures the speed of the built-in file I/O objects returned by open() while performing various operations, and ccbench is a concurrency benchmark that tries to measure computing throughput, thread switching latency, and IO processing bandwidth when performing several tasks using a varying number of threads.
The Tools/i18n/msgfmt.py script now understands plural forms in .po files. (Fixed by Martin von Löwis; bpo-5464.)
When importing a module from a .pyc or .pyo file with an existing .py counterpart, the co_filename attributes of the resulting code objects are overwritten when the original filename is obsolete. This can happen if the file has been renamed, moved, or is accessed through different paths. (Patch by Ziga Seilnacht and Jean-Paul Calderone; bpo-1180193.)
The regrtest.py script now takes a --randseed= switch that takes an integer that will be used as the random seed for the -r option that executes tests in random order. The -r option also reports the seed that was used (Added by Collin Winter.)
Another regrtest.py switch is -j, which takes an integer specifying how many tests run in parallel. This allows reducing the total runtime on multi-core machines. This option is compatible with several other options, including the -R switch which is known to produce long runtimes. (Added by Antoine Pitrou, bpo-6152.) This can also be used with a new -F switch that runs selected tests in a loop until they fail. (Added by Antoine Pitrou; bpo-7312.)
When executed as a script, the py_compile.py module now accepts '-' as an argument, which will read standard input for the list of filenames to be compiled. (Contributed by Piotr Ożarowski; bpo-8233.)

Porting to Python 2.7¶

Esta seção lista as alterações descritas anteriormente e outras correções que podem exigir alterações no seu código.

The range() function processes its arguments more consistently; it will now call __int__() on non-float, non-integer arguments that are supplied to it. (Fixed by Alexander Belopolsky; bpo-1533.)
The string format() method changed the default precision used for floating-point and complex numbers from 6 decimal places to 12, which matches the precision used by str(). (Changed by Eric Smith; bpo-5920.)
Because of an optimization for the with statement, the special methods __enter__() and __exit__() must belong to the object’s type, and cannot be directly attached to the object’s instance. This affects new-style classes (derived from object) and C extension types. (bpo-6101.)
Due to a bug in Python 2.6, the exc_value parameter to __exit__() methods was often the string representation of the exception, not an instance. This was fixed in 2.7, so exc_value will be an instance as expected. (Fixed by Florent Xicluna; bpo-7853.)
Quando um conjunto restrito de atributos foi definido usando __slots__, excluir um atributo não definido não levantaria AttributeError como seria de esperar. Correção de Benjamin Peterson; bpo-7604.)

In the standard library:

Operations with datetime instances that resulted in a year falling outside the supported range didn’t always raise OverflowError. Such errors are now checked more carefully and will now raise the exception. (Reported by Mark Leander, patch by Anand B. Pillai and Alexander Belopolsky; bpo-7150.)
When using Decimal instances with a string’s format() method, the default alignment was previously left-alignment. This has been changed to right-alignment, which might change the output of your programs. (Changed by Mark Dickinson; bpo-6857.)

Comparisons involving a signaling NaN value (or sNAN) now signal InvalidOperation instead of silently returning a true or false value depending on the comparison operator. Quiet NaN values (or NaN) are now hashable. (Fixed by Mark Dickinson; bpo-7279.)
The xml.etree.ElementTree library no longer escapes ampersands and angle brackets when outputting an XML processing instruction (which looks like <?xml-stylesheet href="#style1"?>) or comment (which looks like ). (Patch by Neil Muller; bpo-2746.)
The readline() method of StringIO objects now does nothing when a negative length is requested, as other file-like objects do. (bpo-7348).
The syslog module will now use the value of sys.argv[0] as the identifier instead of the previous default value of 'python'. (Changed by Sean Reifschneider; bpo-8451.)
The tarfile module’s default error handling has changed, to no longer suppress fatal errors. The default error level was previously 0, which meant that errors would only result in a message being written to the debug log, but because the debug log is not activated by default, these errors go unnoticed. The default error level is now 1, which raises an exception if there’s an error. (Changed by Lars Gustäbel; bpo-7357.)
The urlparse module’s urlsplit() now handles unknown URL schemes in a fashion compliant with RFC 3986: if the URL is of the form "<something>://...", the text before the :// is treated as the scheme, even if it’s a made-up scheme that the module doesn’t know about. This change may break code that worked around the old behaviour. For example, Python 2.6.4 or 2.5 will return the following:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', '', '//host/filename?query', '', '')
```
Python 2.7 (and Python 2.6.5) will return:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', 'host', '/filename?query', '', '')
```
(Python 2.7 actually produces slightly different output, since it returns a named tuple instead of a standard tuple.)

For C extensions:

C extensions that use integer format codes with the PyArg_Parse* family of functions will now raise a TypeError exception instead of triggering a DeprecationWarning (bpo-5080).
Use the new PyOS_string_to_double() function instead of the old PyOS_ascii_strtod() and PyOS_ascii_atof() functions, which are now deprecated.

For applications that embed Python:

The PySys_SetArgvEx() function was added, letting applications close a security hole when the existing PySys_SetArgv() function was used. Check whether you’re calling PySys_SetArgv() and carefully consider whether the application should be using PySys_SetArgvEx() with updatepath set to false.

New Features Added to Python 2.7 Maintenance Releases¶

New features may be added to Python 2.7 maintenance releases when the situation genuinely calls for it. Any such additions must go through the Python Enhancement Proposal process, and make a compelling case for why they can’t be adequately addressed by either adding the new feature solely to Python 3, or else by publishing it on the Python Package Index.

In addition to the specific proposals listed below, there is a general exemption allowing new -3 warnings to be added in any Python 2.7 maintenance release.

Two new environment variables for debug mode¶

In debug mode, the [xxx refs] statistic is not written by default, the PYTHONSHOWREFCOUNT environment variable now must also be set. (Contributed by Victor Stinner; bpo-31733.)

When Python is compiled with COUNT_ALLOC defined, allocation counts are no longer dumped by default anymore: the PYTHONSHOWALLOCCOUNT environment variable must now also be set. Moreover, allocation counts are now dumped into stderr, rather than stdout. (Contributed by Victor Stinner; bpo-31692.)

Novo na versão 2.7.15.

PEP 434: IDLE Enhancement Exception for All Branches¶

PEP 434 describes a general exemption for changes made to the IDLE development environment shipped along with Python. This exemption makes it possible for the IDLE developers to provide a more consistent user experience across all supported versions of Python 2 and 3.

For details of any IDLE changes, refer to the NEWS file for the specific release.

PEP 466: Network Security Enhancements for Python 2.7¶

PEP 466 describes a number of network security enhancement proposals that have been approved for inclusion in Python 2.7 maintenance releases, with the first of those changes appearing in the Python 2.7.7 release.

PEP 466 related features added in Python 2.7.7:

hmac.compare_digest() was backported from Python 3 to make a timing attack resistant comparison operation available to Python 2 applications. (Contributed by Alex Gaynor; bpo-21306.)
OpenSSL 1.0.1g was upgraded in the official Windows installers published on python.org. (Contributed by Zachary Ware; bpo-21462.)

PEP 466 relação das características adicionadas no Python 2.7.8:

hashlib.pbkdf2_hmac() was backported from Python 3 to make a hashing algorithm suitable for secure password storage broadly available to Python 2 applications. (Contributed by Alex Gaynor; bpo-21304.)
OpenSSL 1.0.1h was upgraded for the official Windows installers published on python.org. (Contributed by Zachary Ware in bpo-21671 for CVE-2014-0224.)

PEP 466 related features added in Python 2.7.9:

Most of Python 3.4’s ssl module was backported. This means ssl now supports Server Name Indication, TLS1.x settings, access to the platform certificate store, the SSLContext class, and other features. (Contributed by Alex Gaynor and David Reid; bpo-21308.)

Refer to the “Version added: 2.7.9” notes in the module documentation for specific details.
os.urandom() was changed to cache a file descriptor to /dev/urandom instead of reopening /dev/urandom on every call. (Contributed by Alex Gaynor; bpo-21305.)
hashlib.algorithms_guaranteed and hashlib.algorithms_available were backported from Python 3 to make it easier for Python 2 applications to select the strongest available hash algorithm. (Contributed by Alex Gaynor in bpo-21307)

PEP 477: Backport ensurepip (PEP 453) to Python 2.7¶

PEP 477 approves the inclusion of the PEP 453 ensurepip module and the improved documentation that was enabled by it in the Python 2.7 maintenance releases, appearing first in the Python 2.7.9 release.

Bootstrapping pip By Default¶

The new ensurepip module (defined in PEP 453) provides a standard cross-platform mechanism to bootstrap the pip installer into Python installations. The version of pip included with Python 2.7.9 is pip 1.5.6, and future 2.7.x maintenance releases will update the bundled version to the latest version of pip that is available at the time of creating the release candidate.

By default, the commands pip, pipX and pipX.Y will be installed on all platforms (where X.Y stands for the version of the Python installation), along with the pip Python package and its dependencies.

For CPython source builds on POSIX systems, the make install and make altinstall commands do not bootstrap pip by default. This behaviour can be controlled through configure options, and overridden through Makefile options.

On Windows and Mac OS X, the CPython installers now default to installing pip along with CPython itself (users may opt out of installing it during the installation process). Window users will need to opt in to the automatic PATH modifications to have pip available from the command line by default, otherwise it can still be accessed through the Python launcher for Windows as py -m pip.

As discussed in the PEP, platform packagers may choose not to install these commands by default, as long as, when invoked, they provide clear and simple directions on how to install them on that platform (usually using the system package manager).

Mudanças na documentação¶

As part of this change, the Instalando módulos Python and Distribuindo módulos Python sections of the documentation have been completely redesigned as short getting started and FAQ documents. Most packaging documentation has now been moved out to the Python Packaging Authority maintained Python Packaging User Guide and the documentation of the individual projects.

However, as this migration is currently still incomplete, the legacy versions of those guides remaining available as Construindo extensões C e C ++ com setuptools and Construindo extensões C e C ++ com setuptools.

Ver também

PEP 453 – Explicit bootstrapping of pip in Python installations: PEP written by Donald Stufft and Nick Coghlan, implemented by Donald Stufft, Nick Coghlan, Martin von Löwis and Ned Deily.

PEP 476: Ativando a verificação de certificados por padrão para clientes stdlib http¶

PEP 476 updated httplib and modules which use it, such as urllib2 and xmlrpclib, to now verify that the server presents a certificate which is signed by a Certificate Authority in the platform trust store and whose hostname matches the hostname being requested by default, significantly improving security for many applications. This change was made in the Python 2.7.9 release.

Para aplicativos que exigem o antigo comportamento anterior, eles podem passar um contexto alternativo

import urllib2
import ssl

# This disables all verification
context = ssl._create_unverified_context()

# This allows using a specific certificate for the host, which doesn't need
# to be in the trust store
context = ssl.create_default_context(cafile="/path/to/file.crt")

urllib2.urlopen("https://invalid-cert", context=context)

PEP 493: HTTPS verification migration tools for Python 2.7¶

PEP 493 provides additional migration tools to support a more incremental infrastructure upgrade process for environments containing applications and services relying on the historically permissive processing of server certificates when establishing client HTTPS connections. These additions were made in the Python 2.7.12 release.

These tools are intended for use in cases where affected applications and services can’t be modified to explicitly pass a more permissive SSL context when establishing the connection.

For applications and services which can’t be modified at all, the new PYTHONHTTPSVERIFY environment variable may be set to 0 to revert an entire Python process back to the default permissive behaviour of Python 2.7.8 and earlier.

For cases where the connection establishment code can’t be modified, but the overall application can be, the new ssl._https_verify_certificates() function can be used to adjust the default behaviour at runtime.

New `make regen-all` build target¶

To simplify cross-compilation, and to ensure that CPython can reliably be compiled without requiring an existing version of Python to already be available, the autotools-based build system no longer attempts to implicitly recompile generated files based on file modification times.

Instead, a new make regen-all command has been added to force regeneration of these files when desired (e.g. after an initial version of Python has already been built based on the pregenerated versions).

More selective regeneration targets are also defined - see Makefile.pre.in for details.

(Contribuição de Victor Stinner em bpo-23404.)

Novo na versão 2.7.14.

Removal of `make touch` build target¶

The make touch build target previously used to request implicit regeneration of generated files by updating their modification times has been removed.

It has been replaced by the new make regen-all target.

(Contribuição de Victor Stinner em bpo-23404.)

Alterado na versão 2.7.14.

Reconhecimentos¶

The author would like to thank the following people for offering suggestions, corrections and assistance with various drafts of this article: Nick Coghlan, Philip Jenvey, Ryan Lovett, R. David Murray, Hugh Secker-Walker.

O que há de novo no Python 2.7¶

O futuro para o Python 2.x¶

Mudanças no tratamento de avisos de descontinuação¶

Recursos do Python 3.1¶

PEP 372: Adicionando um dicionário ordenado a coleções¶

PEP 378: Especificador de formato para separador de milhares¶

PEP 389: O módulo argparse para analisar linhas de comando¶

PEP 391: Configuração baseada em dicionário para logging¶

PEP 3106: Views de dicionário¶

PEP 3137: O objeto memoryview¶

Outras mudanças na linguagem¶

Alterações do interpretador¶

Otimizações¶

Módulos Novos ou Aprimorados¶

New module: importlib¶

New module: sysconfig¶

ttk: Themed Widgets for Tk¶

Updated module: unittest¶

Updated module: ElementTree 1.3¶

Alterações a compilações e API C¶

Capsules¶

Port-Specific Changes: Windows¶

Port-Specific Changes: Mac OS X¶

Port-Specific Changes: FreeBSD¶

Other Changes and Fixes¶

Porting to Python 2.7¶

New Features Added to Python 2.7 Maintenance Releases¶

Two new environment variables for debug mode¶

PEP 434: IDLE Enhancement Exception for All Branches¶

PEP 466: Network Security Enhancements for Python 2.7¶

PEP 477: Backport ensurepip (PEP 453) to Python 2.7¶

Bootstrapping pip By Default¶

Mudanças na documentação¶

PEP 476: Ativando a verificação de certificados por padrão para clientes stdlib http¶

PEP 493: HTTPS verification migration tools for Python 2.7¶

New make regen-all build target¶

Removal of make touch build target¶

Reconhecimentos¶

New `make regen-all` build target¶

Removal of `make touch` build target¶