1. Linha de comando e ambiente

O interpretador do CPython verifica a linha de comando e o ambiente em busca de várias configurações.

Os esquemas de linha de comando de outras implementações podem ser diferentes. Consulte Implementações Alternativas para mais recursos.

1.1. Linha de comando

Ao invocar o Python, você pode especificar qualquer uma destas opções:

python [-bBdEhiIOqsSuvVWx?] [-c command | -m module-name | script | - ] [args]

O caso de uso mais comum é, obviamente, uma simples invocação de um script:

python myscript.py

1.1.1. Opções de interface

A interface do interpretador é semelhante à do console do UNIX, mas fornece alguns métodos adicionais de chamada:

• Quando chamado com a entrada padrão conectada a um dispositivo tty, ele solicita comandos e os executa até um EOF (um caractere de fim de arquivo, você pode produzi-lo com Ctrl-D no UNIX ou Ctrl-Z, Enter no Windows) ser lido.
• Quando chamado com um argumento de nome de arquivo ou com um arquivo como entrada padrão, ele lê e executa um script desse arquivo.
• Quando chamado com um argumento de nome de diretório, ele lê e executa um script nomeado adequadamente desse diretório.
• Quando chamado com -c command, ele executa as instruções Python fornecidas como command. Aqui command pode conter várias instruções separadas por novas linhas. O espaço em branco à esquerda é significativo nas instruções do Python!
• Quando chamado com -m module-name, o módulo fornecido está localizado no caminho do módulo Python e é executado como um script.

No modo não interativo, toda a entrada é analisada antes de ser executada.

Uma opção de interface termina a lista de opções consumidas pelo interpretador, todos os argumentos consecutivos terminam em sys.argv – observe que o primeiro elemento, subscrito zero (sys.argv[0]) , é uma string que reflete a fonte do programa.

-c <command>

Executa o código Python em command. command pode ser uma ou mais instruções separadas por novas linhas, com espaços em branco à esquerda significativos, como no código normal do módulo.

Se esta opção for fornecida, o primeiro elemento de sys.argv será "-c" e o diretório atual será adicionado ao início de sys.path (permitindo módulos nesse diretório para ser importado como módulos de nível superior).

-m <module-name>

Procura sys.path pelo módulo nomeado e executa seu conteúdo como o módulo __main__.

Como o argumento é um nome de module, você não deve fornecer uma extensão de arquivo (.py). O nome do módulo deve ser um nome de módulo Python absoluto válido, mas a implementação nem sempre pode impor isso (por exemplo, pode permitir que você use um nome que inclua um hífen).

Nomes de pacotes (incluindo pacotes de espaço de nomes) também são permitidos. Quando um nome de pacote é fornecido ao invés de um módulo normal, o interpretador irá executar <pkg>.__main__ como o módulo principal. Esse comportamento é deliberadamente semelhante ao tratamento de diretórios e arquivos zip que são passados para o interpretador como o argumento do script.

Nota

Esta opção não pode ser usada com módulos embutidos e módulos de extensão escritos em C, uma vez que eles não possuem arquivos de módulo Python. No entanto, ele ainda pode ser usado para módulos pré-compilados, mesmo se o arquivo fonte original não estiver disponível.

Se esta opção for fornecida, o primeiro elemento de sys.argv será o caminho completo para o arquivo do módulo (enquanto o arquivo do módulo está sendo localizado, o primeiro elemento será definido como "-m"). Como com a opção -c, o diretório atual será adicionado ao início de sys.path.

Muitos módulos de biblioteca padrão contêm código que é chamado em sua execução como um script. Um exemplo é o módulo timeit:

python -mtimeit -s 'setup here' 'benchmarked code here'
python -mtimeit -h # for details

Ver também

runpy.run_module()

Funcionalidade equivalente diretamente disponível para o código Python

PEP 338 – Executando módulos como scripts

Alterado na versão 3.1: Forneça o nome do pacote para executar um submódulo __main__.

Alterado na versão 3.4: pacotes de espaço de nomes também são suportados

-

Lê os comandos da entrada padrão (sys.stdin). Se a entrada padrão for um terminal, -i está implícito.

Se esta opção for fornecida, o primeiro elemento de sys.argv será "-" e o diretório atual será adicionado ao início de sys.path.

<script>

Execute the Python code contained in script, which must be a filesystem path (absolute or relative) referring to either a Python file, a directory containing a __main__.py file, or a zipfile containing a __main__.py file.

If this option is given, the first element of sys.argv will be the script name as given on the command line.

If the script name refers directly to a Python file, the directory containing that file is added to the start of sys.path, and the file is executed as the __main__ module.

If the script name refers to a directory or zipfile, the script name is added to the start of sys.path and the __main__.py file in that location is executed as the __main__ module.

Ver também

runpy.run_path()

Funcionalidade equivalente diretamente disponível para o código Python

If no interface option is given, -i is implied, sys.argv[0] is an empty string ("") and the current directory will be added to the start of sys.path. Also, tab-completion and history editing is automatically enabled, if available on your platform (see Configuração Readline).

Ver também

Chamando o interpretador

Alterado na versão 3.4: Automatic enabling of tab-completion and history editing.

1.1.2. Opções genéricas

-?

-h

--help

Print a short description of all command line options.

-V

--version

Print the Python version number and exit. Example output could be:

Python 3.0

1.1.3. Miscellaneous options

-b

Issue a warning when comparing bytes or bytearray with str or bytes with int. Issue an error when the option is given twice (-bb).

Alterado na versão 3.5: Affects comparisons of bytes with int.

-B

If given, Python won’t try to write .pyc files on the import of source modules. See also PYTHONDONTWRITEBYTECODE.

-d

Turn on parser debugging output (for wizards only, depending on compilation options). See also PYTHONDEBUG.

-E

Ignore all PYTHON* environment variables, e.g. PYTHONPATH and PYTHONHOME, that might be set.

-i

When a script is passed as first argument or the -c option is used, enter interactive mode after executing the script or the command, even when sys.stdin does not appear to be a terminal. The PYTHONSTARTUP file is not read.

This can be useful to inspect global variables or a stack trace when a script raises an exception. See also PYTHONINSPECT.

-I

Run Python in isolated mode. This also implies -E and -s. In isolated mode sys.path contains neither the script’s directory nor the user’s site-packages directory. All PYTHON* environment variables are ignored, too. Further restrictions may be imposed to prevent the user from injecting malicious code.

Novo na versão 3.4.

-O

Turn on basic optimizations. See also PYTHONOPTIMIZE.

-OO

Discard docstrings in addition to the -O optimizations.

-q

Não exibe as mensagens de copyright e de versão nem mesmo no modo interativo.

Novo na versão 3.2.

-R

Kept for compatibility. On Python 3.3 and greater, hash randomization is turned on by default.

On previous versions of Python, this option turns on hash randomization, so that the __hash__() values of str, bytes and datetime are “salted” with an unpredictable random value. Although they remain constant within an individual Python process, they are not predictable between repeated invocations of Python.

Hash randomization is intended to provide protection against a denial-of-service caused by carefully-chosen inputs that exploit the worst case performance of a dict construction, O(n^2) complexity. See http://www.ocert.org/advisories/ocert-2011-003.html for details.

PYTHONHASHSEED allows you to set a fixed value for the hash seed secret.

Novo na versão 3.2.3.

-s

Don’t add the user site-packages directory to sys.path.

Ver também

PEP 370 – Per user site-packages directory

-S

Disable the import of the module site and the site-dependent manipulations of sys.path that it entails. Also disable these manipulations if site is explicitly imported later (call site.main() if you want them to be triggered).

-u

Force the binary layer of the stdout and stderr streams (which is available as their buffer attribute) to be unbuffered. The text I/O layer will still be line-buffered if writing to the console, or block-buffered if redirected to a non-interactive file.

See also PYTHONUNBUFFERED.

-v

Print a message each time a module is initialized, showing the place (filename or built-in module) from which it is loaded. When given twice (-vv), print a message for each file that is checked for when searching for a module. Also provides information on module cleanup at exit. See also PYTHONVERBOSE.

-W arg

Warning control. Python’s warning machinery by default prints warning messages to sys.stderr. A typical warning message has the following form:

file:line: category: message

By default, each warning is printed once for each source line where it occurs. This option controls how often warnings are printed.

Multiple -W options may be given; when a warning matches more than one option, the action for the last matching option is performed. Invalid -W options are ignored (though, a warning message is printed about invalid options when the first warning is issued).

Warnings can also be controlled from within a Python program using the warnings module.

The simplest form of argument is one of the following action strings (or a unique abbreviation):

ignore

Ignore todas as advertências..

default

Explicitly request the default behavior (printing each warning once per source line).

all

Print a warning each time it occurs (this may generate many messages if a warning is triggered repeatedly for the same source line, such as inside a loop).

module

Print each warning only the first time it occurs in each module.

once

Print each warning only the first time it occurs in the program.

error

Raise an exception instead of printing a warning message.

The full form of argument is:

action:message:category:module:line

Here, action is as explained above but only applies to messages that match the remaining fields. Empty fields match all values; trailing empty fields may be omitted. The message field matches the start of the warning message printed; this match is case-insensitive. The category field matches the warning category. This must be a class name; the match tests whether the actual warning category of the message is a subclass of the specified warning category. The full class name must be given. The module field matches the (fully-qualified) module name; this match is case-sensitive. The line field matches the line number, where zero matches all line numbers and is thus equivalent to an omitted line number.

Ver também

warnings – the warnings module

PEP 230 – Warning framework

PYTHONWARNINGS

-x

Skip the first line of the source, allowing use of non-Unix forms of #!cmd. This is intended for a DOS specific hack only.

Nota

The line numbers in error messages will be off by one.

-X

Reserved for various implementation-specific options. CPython currently defines the following possible values:

• -X faulthandler to enable faulthandler;
• -X showrefcount to enable the output of the total reference count and memory blocks (only works on debug builds);
• -X tracemalloc to start tracing Python memory allocations using the tracemalloc module. By default, only the most recent frame is stored in a traceback of a trace. Use -X tracemalloc=NFRAME to start tracing with a traceback limit of NFRAME frames. See the tracemalloc.start() for more information.

It also allows passing arbitrary values and retrieving them through the sys._xoptions dictionary.

Alterado na versão 3.2: It is now allowed to pass -X with CPython.

Novo na versão 3.3: The -X faulthandler option.

Novo na versão 3.4: The -X showrefcount and -X tracemalloc options.

1.1.4. Options you shouldn’t use

-J

Reserved for use by Jython.

1.2. Environment variables

These environment variables influence Python’s behavior, they are processed before the command-line switches other than -E or -I. It is customary that command-line switches override environmental variables where there is a conflict.

PYTHONHOME

Change the location of the standard Python libraries. By default, the libraries are searched in prefix/lib/pythonversion and exec_prefix/lib/pythonversion, where prefix and exec_prefix are installation-dependent directories, both defaulting to /usr/local.

When PYTHONHOME is set to a single directory, its value replaces both prefix and exec_prefix. To specify different values for these, set PYTHONHOME to prefix:exec_prefix.

PYTHONPATH

Augment the default search path for module files. The format is the same as the shell’s PATH: one or more directory pathnames separated by os.pathsep (e.g. colons on Unix or semicolons on Windows). Non-existent directories are silently ignored.

In addition to normal directories, individual PYTHONPATH entries may refer to zipfiles containing pure Python modules (in either source or compiled form). Extension modules cannot be imported from zipfiles.

The default search path is installation dependent, but generally begins with prefix/lib/pythonversion (see PYTHONHOME above). It is always appended to PYTHONPATH.

An additional directory will be inserted in the search path in front of PYTHONPATH as described above under Opções de interface. The search path can be manipulated from within a Python program as the variable sys.path.

PYTHONSTARTUP

If this is the name of a readable file, the Python commands in that file are executed before the first prompt is displayed in interactive mode. The file is executed in the same namespace where interactive commands are executed so that objects defined or imported in it can be used without qualification in the interactive session. You can also change the prompts sys.ps1 and sys.ps2 and the hook sys.__interactivehook__ in this file.

PYTHONOPTIMIZE

If this is set to a non-empty string it is equivalent to specifying the -O option. If set to an integer, it is equivalent to specifying -O multiple times.

PYTHONDEBUG

If this is set to a non-empty string it is equivalent to specifying the -d option. If set to an integer, it is equivalent to specifying -d multiple times.

PYTHONINSPECT

If this is set to a non-empty string it is equivalent to specifying the -i option.

This variable can also be modified by Python code using os.environ to force inspect mode on program termination.

PYTHONUNBUFFERED

If this is set to a non-empty string it is equivalent to specifying the -u option.

PYTHONVERBOSE

If this is set to a non-empty string it is equivalent to specifying the -v option. If set to an integer, it is equivalent to specifying -v multiple times.

PYTHONCASEOK

If this is set, Python ignores case in import statements. This only works on Windows and OS X.

PYTHONDONTWRITEBYTECODE

If this is set to a non-empty string, Python won’t try to write .pyc files on the import of source modules. This is equivalent to specifying the -B option.

PYTHONHASHSEED

If this variable is not set or set to random, a random value is used to seed the hashes of str, bytes and datetime objects.

If PYTHONHASHSEED is set to an integer value, it is used as a fixed seed for generating the hash() of the types covered by the hash randomization.

Its purpose is to allow repeatable hashing, such as for selftests for the interpreter itself, or to allow a cluster of python processes to share hash values.

The integer must be a decimal number in the range [0,4294967295]. Specifying the value 0 will disable hash randomization.

Novo na versão 3.2.3.

PYTHONIOENCODING

If this is set before running the interpreter, it overrides the encoding used for stdin/stdout/stderr, in the syntax encodingname:errorhandler. Both the encodingname and the :errorhandler parts are optional and have the same meaning as in str.encode().

For stderr, the :errorhandler part is ignored; the handler will always be 'backslashreplace'.

Alterado na versão 3.4: The encodingname part is now optional.

PYTHONNOUSERSITE

If this is set, Python won’t add the user site-packages directory to sys.path.

Ver também

PEP 370 – Per user site-packages directory

PYTHONUSERBASE

Defines the user base directory, which is used to compute the path of the user site-packages directory and Distutils installation paths for python setup.py install --user.

Ver também

PEP 370 – Per user site-packages directory

PYTHONEXECUTABLE

If this environment variable is set, sys.argv[0] will be set to its value instead of the value got through the C runtime. Only works on Mac OS X.

PYTHONWARNINGS

This is equivalent to the -W option. If set to a comma separated string, it is equivalent to specifying -W multiple times.

PYTHONFAULTHANDLER

If this environment variable is set to a non-empty string, faulthandler.enable() is called at startup: install a handler for SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL signals to dump the Python traceback. This is equivalent to -X faulthandler option.

Novo na versão 3.3.

PYTHONTRACEMALLOC

If this environment variable is set to a non-empty string, start tracing Python memory allocations using the tracemalloc module. The value of the variable is the maximum number of frames stored in a traceback of a trace. For example, PYTHONTRACEMALLOC=1 stores only the most recent frame. See the tracemalloc.start() for more information.

Novo na versão 3.4.

PYTHONASYNCIODEBUG

If this environment variable is set to a non-empty string, enable the debug mode of the asyncio module.

Novo na versão 3.4.

1.2.1. Debug-mode variables

Setting these variables only has an effect in a debug build of Python, that is, if Python was configured with the --with-pydebug build option.

PYTHONTHREADDEBUG

If set, Python will print threading debug info.

PYTHONDUMPREFS

If set, Python will dump objects and reference counts still alive after shutting down the interpreter.

PYTHONMALLOCSTATS

If set, Python will print memory allocation statistics every time a new object arena is created, and on shutdown.