1. Linha de comando e ambiente¶

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

CPython implementation detail: 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).

Levanta um evento de auditoria cpython.run_command com argumento command.

-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.

A opção -I pode ser usada para executar o script em modo isolado onde sys.path não contém nem o diretório atual nem o diretório de pacotes de sites do usuário. Todas as variáveis de ambiente PYTHON* são ignoradas também.

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

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

Levanta um evento de auditoria cpython.run_module com argumento module-name.

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.

Levanta um evento de auditoria cpython.run_stdin com nenhum argumento.

<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.

-I option can be used to run the script in isolated mode where sys.path contains neither the script’s directory nor the user’s site-packages directory. All PYTHON* environment variables are ignored, too.

Raises an auditing event cpython.run_file with argument filename.

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 3.8.0b2+

When given twice, print more information about the build, like:

Python 3.8.0b2+ (3.8:0c076caaa8, Apr 20 2019, 21:55:00)
[GCC 6.2.0 20161005]

Novo na versão 3.6: The -VV option.

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.

--check-hash-based-pycs default|always|never¶

Control the validation behavior of hash-based .pyc files. See Cached bytecode invalidation. When set to default, checked and unchecked hash-based bytecode cache files are validated according to their default semantics. When set to always, all hash-based .pyc files, whether checked or unchecked, are validated against their corresponding source file. When set to never, hash-based .pyc files are not validated against their corresponding source files.

The semantics of timestamp-based .pyc files are unaffected by this option.

-d¶: Turn on parser debugging output (for expert 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¶: Remove assert statements and any code conditional on the value of __debug__. Augment the filename for compiled (bytecode) files by adding .opt-1 before the .pyc extension (see PEP 488). See also PYTHONOPTIMIZE.

Alterado na versão 3.5: Modify .pyc filenames according to PEP 488.

-OO¶: Do -O and also discard docstrings. Augment the filename for compiled (bytecode) files by adding .opt-2 before the .pyc extension (see PEP 488).

Alterado na versão 3.5: Modify .pyc filenames according to PEP 488.

-q¶: Não exibe as mensagens de copyright e de versão nem mesmo no modo interativo.

Novo na versão 3.2.

-R¶

Turn on hash randomization. This option only has an effect if the PYTHONHASHSEED environment variable is set to 0, since hash randomization is enabled by default.

On previous versions of Python, this option turns on hash randomization, so that the __hash__() values of str and bytes objects 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.

Alterado na versão 3.7: A opção não é mais ignorada.

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 stdout and stderr streams to be unbuffered. This option has no effect on the stdin stream.

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.

PYTHONPLATLIBDIR¶: If this is set to a non-empty string, it overrides the sys.platlibdir value.

Novo na versão 3.9.

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.

Raises an auditing event cpython.run_startup with the filename as the argument when called on startup.

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.

PYTHONBREAKPOINT¶: If this is set, it names a callable using dotted-path notation. The module containing the callable will be imported and then the callable will be run by the default implementation of sys.breakpointhook() which itself is called by built-in breakpoint(). If not set, or set to the empty string, it is equivalent to the value “pdb.set_trace”. Setting this to the string “0” causes the default implementation of sys.breakpointhook() to do nothing but return immediately.

Novo na versão 3.7.

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.

PYTHONOLDPARSER¶

If this is set to a non-empty string, enable the traditional LL(1) parser.

See also the -X oldparser option and PEP 617.

Deprecated since version 3.9, will be removed in version 3.10.

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.

PYTHONPYCACHEPREFIX¶: If this is set, Python will write .pyc files in a mirror directory tree at this path, instead of in __pycache__ directories within the source tree. This is equivalent to specifying the -X pycache_prefix=PATH option.

Novo na versão 3.8.

PYTHONHASHSEED¶

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

Alterado na versão 3.6: On Windows, the encoding specified by this variable is ignored for interactive console buffers unless PYTHONLEGACYWINDOWSSTDIO is also specified. Files and pipes redirected through the standard streams are not affected.

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, with filters later in the list taking precedence over those earlier in the list.

The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default):

PYTHONWARNINGS=default  # Warn once per call location
PYTHONWARNINGS=error    # Convert to exceptions
PYTHONWARNINGS=always   # Warn every time
PYTHONWARNINGS=module   # Warn once per calling module
PYTHONWARNINGS=once     # Warn once per Python process
PYTHONWARNINGS=ignore   # Never warn

See The Warnings Filter and Describing Warning Filters for more details.

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.

PYTHONPROFILEIMPORTTIME¶: If this environment variable is set to a non-empty string, Python will show how long each import takes. This is exactly equivalent to setting -X importtime on the command line.

Novo na versão 3.7.

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.

PYTHONMALLOC¶

Set the Python memory allocators and/or install debug hooks.

Set the family of memory allocators used by Python:

default: use the default memory allocators.
malloc: use the malloc() function of the C library for all domains (PYMEM_DOMAIN_RAW, PYMEM_DOMAIN_MEM, PYMEM_DOMAIN_OBJ).
pymalloc: use the pymalloc allocator for PYMEM_DOMAIN_MEM and PYMEM_DOMAIN_OBJ domains and use the malloc() function for the PYMEM_DOMAIN_RAW domain.

Install debug hooks:

debug: install debug hooks on top of the default memory allocators.
malloc_debug: same as malloc but also install debug hooks.
pymalloc_debug: same as pymalloc but also install debug hooks.

See the default memory allocators and the PyMem_SetupDebugHooks() function (install debug hooks on Python memory allocators).

Alterado na versão 3.7: Added the "default" allocator.

Novo na versão 3.6.

PYTHONMALLOCSTATS¶

If set to a non-empty string, Python will print statistics of the pymalloc memory allocator every time a new pymalloc object arena is created, and on shutdown.

This variable is ignored if the PYTHONMALLOC environment variable is used to force the malloc() allocator of the C library, or if Python is configured without pymalloc support.

Alterado na versão 3.6: This variable can now also be used on Python compiled in release mode. It now has no effect if set to an empty string.

PYTHONLEGACYWINDOWSFSENCODING¶

If set to a non-empty string, the default filesystem encoding and errors mode will revert to their pre-3.6 values of ‘mbcs’ and ‘replace’, respectively. Otherwise, the new defaults ‘utf-8’ and ‘surrogatepass’ are used.

This may also be enabled at runtime with sys._enablelegacywindowsfsencoding().

Disponibilidade: Windows.

Novo na versão 3.6: Veja PEP 529 para mais detalhes.

PYTHONLEGACYWINDOWSSTDIO¶

If set to a non-empty string, does not use the new console reader and writer. This means that Unicode characters will be encoded according to the active console code page, rather than using utf-8.

This variable is ignored if the standard streams are redirected (to files or pipes) rather than referring to console buffers.

Disponibilidade: Windows.

Novo na versão 3.6.

PYTHONCOERCECLOCALE¶

If set to the value 0, causes the main Python command line application to skip coercing the legacy ASCII-based C and POSIX locales to a more capable UTF-8 based alternative.

If this variable is not set (or is set to a value other than 0), the LC_ALL locale override environment variable is also not set, and the current locale reported for the LC_CTYPE category is either the default C locale, or else the explicitly ASCII-based POSIX locale, then the Python CLI will attempt to configure the following locales for the LC_CTYPE category in the order listed before loading the interpreter runtime:

C.UTF-8
C.utf8
UTF-8

If setting one of these locale categories succeeds, then the LC_CTYPE environment variable will also be set accordingly in the current process environment before the Python runtime is initialized. This ensures that in addition to being seen by both the interpreter itself and other locale-aware components running in the same process (such as the GNU readline library), the updated setting is also seen in subprocesses (regardless of whether or not those processes are running a Python interpreter), as well as in operations that query the environment rather than the current C locale (such as Python’s own locale.getdefaultlocale()).

Configuring one of these locales (either explicitly or via the above implicit locale coercion) automatically enables the surrogateescape error handler for sys.stdin and sys.stdout (sys.stderr continues to use backslashreplace as it does in any other locale). This stream handling behavior can be overridden using PYTHONIOENCODING as usual.

For debugging purposes, setting PYTHONCOERCECLOCALE=warn will cause Python to emit warning messages on stderr if either the locale coercion activates, or else if a locale that would have triggered coercion is still active when the Python runtime is initialized.

Also note that even when locale coercion is disabled, or when it fails to find a suitable target locale, PYTHONUTF8 will still activate by default in legacy ASCII-based locales. Both features must be disabled in order to force the interpreter to use ASCII instead of UTF-8 for system interfaces.

Availability: *nix.

Novo na versão 3.7: See PEP 538 for more details.

PYTHONDEVMODE¶: If this environment variable is set to a non-empty string, enable Python Development Mode, introducing additional runtime checks that are too expensive to be enabled by default.

Novo na versão 3.7.

PYTHONUTF8¶

If set to 1, enables the interpreter’s UTF-8 mode, where UTF-8 is used as the text encoding for system interfaces, regardless of the current locale setting.

This means that:

sys.getfilesystemencoding() returns 'UTF-8' (the locale encoding is ignored).

locale.getpreferredencoding() returns 'UTF-8' (the locale encoding is ignored, and the function’s do_setlocale parameter has no effect).

sys.stdin, sys.stdout, and sys.stderr all use UTF-8 as their text encoding, with the surrogateescape error handler being enabled for sys.stdin and sys.stdout (sys.stderr continues to use backslashreplace as it does in the default locale-aware mode)

As a consequence of the changes in those lower level APIs, other higher level APIs also exhibit different default behaviours:

Command line arguments, environment variables and filenames are decoded to text using the UTF-8 encoding.

os.fsdecode() and os.fsencode() use the UTF-8 encoding.

open(), io.open(), and codecs.open() use the UTF-8 encoding by default. However, they still use the strict error handler by default so that attempting to open a binary file in text mode is likely to raise an exception rather than producing nonsense data.

Note that the standard stream settings in UTF-8 mode can be overridden by PYTHONIOENCODING (just as they can be in the default locale-aware mode).

If set to 0, the interpreter runs in its default locale-aware mode.

Setting any other non-empty string causes an error during interpreter initialisation.

If this environment variable is not set at all, then the interpreter defaults to using the current locale settings, unless the current locale is identified as a legacy ASCII-based locale (as described for PYTHONCOERCECLOCALE), and locale coercion is either disabled or fails. In such legacy locales, the interpreter will default to enabling UTF-8 mode unless explicitly instructed not to do so.

Also available as the -X utf8 option.

Novo na versão 3.7: See PEP 540 for more details.

1.2.1. Debug-mode variables¶

Setting these variables only has an effect in a debug build of Python.

PYTHONTHREADDEBUG¶

If set, Python will print threading debug info.

Need Python configured with the --with-pydebug build option.

PYTHONDUMPREFS¶

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

Need Python configured with the --with-trace-refs build option.

1. Linha de comando e ambiente¶

1.1. Linha de comando¶

1.1.1. Opções de interface¶

1.1.2. Opções genéricas¶

1.1.3. Miscellaneous options¶

1.1.4. Options you shouldn’t use¶

1.2. Environment variables¶

1.2.1. Debug-mode variables¶

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