1. 命令列與環境

The CPython interpreter scans the command line and the environment for various settings.

CPython 實作細節： Other implementations' command line schemes may differ. See 可選實作 for further resources.

1.1. 命令列

When invoking Python, you may specify any of these options:

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

The most common use case is, of course, a simple invocation of a script:

python myscript.py

1.1.1. 介面選項

The interpreter interface resembles that of the UNIX shell, but provides some additional methods of invocation:

  • When called with standard input connected to a tty device, it prompts for commands and executes them until an EOF (an end-of-file character, you can produce that with Ctrl-D on UNIX or Ctrl-Z, Enter on Windows) is read. For more on interactive mode, see 互動模式.

  • When called with a file name argument or with a file as standard input, it reads and executes a script from that file.

  • When called with a directory name argument, it reads and executes an appropriately named script from that directory.

  • When called with -c command, it executes the Python statement(s) given as command. Here command may contain multiple statements separated by newlines. Leading whitespace is significant in Python statements!

  • When called with -m module-name, the given module is located on the Python module path and executed as a script.

In non-interactive mode, the entire input is parsed before it is executed.

An interface option terminates the list of options consumed by the interpreter, all consecutive arguments will end up in sys.argv -- note that the first element, subscript zero (sys.argv[0]), is a string reflecting the program's source.

-c <command>

Execute the Python code in command. command can be one or more statements separated by newlines, with significant leading whitespace as in normal module code.

If this option is given, the first element of sys.argv will be "-c" and the current directory will be added to the start of sys.path (allowing modules in that directory to be imported as top level modules).

引發一個附帶引數 command 的稽核事件 cpython.run_command。

在 3.14 版的變更: command is automatically dedented before execution.

-m <module-name>

Search sys.path for the named module and execute its contents as the __main__ module.

Since the argument is a module name, you must not give a file extension (.py). The module name should be a valid absolute Python module name, but the implementation may not always enforce this (e.g. it may allow you to use a name that includes a hyphen).

Package names (including namespace packages) are also permitted. When a package name is supplied instead of a normal module, the interpreter will execute <pkg>.__main__ as the main module. This behaviour is deliberately similar to the handling of directories and zipfiles that are passed to the interpreter as the script argument.

備註

This option cannot be used with built-in modules and extension modules written in C, since they do not have Python module files. However, it can still be used for precompiled modules, even if the original source file is not available.

If this option is given, the first element of sys.argv will be the full path to the module file (while the module file is being located, the first element will be set to "-m"). As with the -c option, the current directory will be added to the start of sys.path.

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

Many standard library modules contain code that is invoked on their execution as a script. An example is the timeit module:

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

引發一個附帶引數 module-name 的稽核事件 cpython.run_module。

也參考

runpy.run_module()

Equivalent functionality directly available to Python code

PEP 338 -- Executing modules as scripts

在 3.1 版的變更: Supply the package name to run a __main__ submodule.

在 3.4 版的變更: namespace packages are also supported

-

Read commands from standard input (sys.stdin). If standard input is a terminal, -i is implied.

If this option is given, the first element of sys.argv will be "-" and the current directory will be added to the start of sys.path.

引發一個不附帶引數的稽核事件 cpython.run_stdin。

<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.

引發一個附帶引數 filename 的稽核事件 cpython.run_file。

也參考

runpy.run_path()

Equivalent functionality directly available to Python code

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 Readline configuration).

也參考

啟動直譯器

在 3.4 版的變更: Automatic enabling of tab-completion and history editing.

1.1.2. Generic options

-?
-h
--help

Print a short description of all command line options and corresponding environment variables and exit.

--help-env

Print a short description of Python-specific environment variables and exit.

在 3.11 版被加入.

--help-xoptions

Print a description of implementation-specific -X options and exit.

在 3.11 版被加入.

--help-all

印出完整使用資訊並離開。

在 3.11 版被加入.

-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]

在 3.6 版被加入: -VV 選項

1.1.3. Miscellaneous options

-b

Issue a warning when converting bytes or bytearray to str without specifying encoding or comparing bytes or bytearray with str or bytes with int. Issue an error when the option is given twice (-bb).

在 3.5 版的變更: Affects also 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 被快取的位元組碼的無效化. 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). See also the PYTHONDEBUG environment variable.

This option requires a debug build of Python, otherwise it's ignored.

-E

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

另請參閱 -P 和 -I (isolated) 選項。

-i

Enter interactive mode after execution.

Using the -i option will enter interactive mode in any of the following circumstances:

  • When a script is passed as first argument

  • When the -c option is used

  • When the -m option is used

Interactive mode will start 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, -P and -s options.

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.

在 3.4 版被加入.

-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.

在 3.5 版的變更: 根據 PEP 488 修改 .pyc 檔案名稱。

-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).

在 3.5 版的變更: 根據 PEP 488 修改 .pyc 檔案名稱。

-P

Don't prepend a potentially unsafe path to sys.path:

  • python -m module command line: Don't prepend the current working directory.

  • python script.py command line: Don't prepend the script's directory. If it's a symbolic link, resolve symbolic links.

  • python -c code and python (REPL) command lines: Don't prepend an empty string, which means the current working directory.

See also the PYTHONSAFEPATH environment variable, and -E and -I (isolated) options.

在 3.11 版被加入.

-q

Don't display the copyright and version messages even in interactive mode.

在 3.2 版被加入.

-R

Turn on hash randomization. This option only has an effect if the PYTHONHASHSEED environment variable is set to anything other than random, 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(n2) complexity. See https://ocert.org/advisories/ocert-2011-003.html for details.

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

在 3.2.3 版被加入.

在 3.7 版的變更: The option is no longer ignored.

-s

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

另請參閱 PYTHONNOUSERSITE。

也參考

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.

另請參閱 PYTHONUNBUFFERED。

在 3.7 版的變更: The text layer of the stdout and stderr streams now is unbuffered.

-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.

在 3.10 版的變更: The site module reports the site-specific paths and .pth files being processed.

另請參閱 PYTHONVERBOSE。

-W arg

Warning control. Python's warning machinery by default prints warning messages to sys.stderr.

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

-Wdefault  # Warn once per call location
-Werror    # Convert to exceptions
-Walways   # Warn every time
-Wall      # Same as -Walways
-Wmodule   # Warn once per calling module
-Wonce     # Warn once per Python process
-Wignore   # Never warn

The action names can be abbreviated as desired and the interpreter will resolve them to the appropriate action name. For example, -Wi is the same as -Wignore.

完整的引數形式為：

action:message:category:module:lineno

Empty fields match all values; trailing empty fields may be omitted. For example -W ignore::DeprecationWarning ignores all DeprecationWarning warnings.

The action field is as explained above but only applies to warnings that match the remaining fields.

The message field must match the whole warning message; this match is case-insensitive.

The category field matches the warning category (ex: DeprecationWarning). This must be a class name; the match test whether the actual warning category of the message is a subclass of the specified warning category.

The module field matches the (fully qualified) module name; this match is case-sensitive.

The lineno field matches the line number, where zero matches all line numbers and is thus equivalent to an omitted line number.

Multiple -W options can 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 using the PYTHONWARNINGS environment variable and from within a Python program using the warnings module. For example, the warnings.filterwarnings() function can be used to use a regular expression on the warning message.

See 警告過濾器 and 描述警告過濾器 for more details.

-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.

-X

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

  • -X faulthandler to enable faulthandler. See also PYTHONFAULTHANDLER.

    在 3.3 版被加入.

  • -X showrefcount to output the total reference count and number of used memory blocks when the program finishes or after each statement in the interactive interpreter. This only works on debug builds.

    在 3.4 版被加入.

  • -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 tracemalloc.start() and PYTHONTRACEMALLOC for more information.

    在 3.4 版被加入.

  • -X int_max_str_digits configures the integer string conversion length limitation. See also PYTHONINTMAXSTRDIGITS.

    在 3.11 版被加入.

  • -X importtime to show how long each import takes. It shows module name, cumulative time (including nested imports) and self time (excluding nested imports). Note that its output may be broken in multi-threaded application. Typical usage is python -X importtime -c 'import asyncio'.

    -X importtime=2 enables additional output that indicates when an imported module has already been loaded. In such cases, the string cached will be printed in both time columns.

    另請參閱 PYTHONPROFILEIMPORTTIME。

    在 3.7 版被加入.

    在 3.14 版的變更: Added -X importtime=2 to also trace imports of loaded modules, and reserved values other than 1 and 2 for future use.

  • -X dev: enable Python Development Mode, introducing additional runtime checks that are too expensive to be enabled by default. See also PYTHONDEVMODE.

    在 3.7 版被加入.

  • -X utf8 enables the Python UTF-8 Mode. -X utf8=0 explicitly disables Python UTF-8 Mode (even when it would otherwise activate automatically). See also PYTHONUTF8.

    在 3.7 版被加入.

  • -X pycache_prefix=PATH enables writing .pyc files to a parallel tree rooted at the given directory instead of to the code tree. See also PYTHONPYCACHEPREFIX.

    在 3.8 版被加入.

  • -X warn_default_encoding issues a EncodingWarning when the locale-specific default encoding is used for opening files. See also PYTHONWARNDEFAULTENCODING.

    在 3.10 版被加入.

  • -X no_debug_ranges disables the inclusion of the tables mapping extra location information (end line, start column offset and end column offset) to every instruction in code objects. This is useful when smaller code objects and pyc files are desired as well as suppressing the extra visual location indicators when the interpreter displays tracebacks. See also PYTHONNODEBUGRANGES.

    在 3.11 版被加入.

  • -X frozen_modules determines whether or not frozen modules are ignored by the import machinery. A value of on means they get imported and off means they are ignored. The default is on if this is an installed Python (the normal case). If it's under development (running from the source tree) then the default is off. Note that the importlib_bootstrap and importlib_bootstrap_external frozen modules are always used, even if this flag is set to off. See also PYTHON_FROZEN_MODULES.

    在 3.11 版被加入.

  • -X perf enables support for the Linux perf profiler. When this option is provided, the perf profiler will be able to report Python calls. This option is only available on some platforms and will do nothing if is not supported on the current system. The default value is "off". See also PYTHONPERFSUPPORT and Python 對 Linux perf 分析器的支援.

    在 3.12 版被加入.

  • -X perf_jit enables support for the Linux perf profiler with DWARF support. When this option is provided, the perf profiler will be able to report Python calls using DWARF information. This option is only available on some platforms and will do nothing if is not supported on the current system. The default value is "off". See also PYTHON_PERF_JIT_SUPPORT and Python 對 Linux perf 分析器的支援.

    在 3.13 版被加入.

  • -X disable_remote_debug disables the remote debugging support as described in PEP 768. This includes both the functionality to schedule code for execution in another process and the functionality to receive code for execution in the current process.

    This option is only available on some platforms and will do nothing if is not supported on the current system. See also PYTHON_DISABLE_REMOTE_DEBUG and PEP 768.

    在 3.14 版被加入.

  • -X cpu_count=n overrides os.cpu_count(), os.process_cpu_count(), and multiprocessing.cpu_count(). n must be greater than or equal to 1. This option may be useful for users who need to limit CPU resources of a container system. See also PYTHON_CPU_COUNT. If n is default, nothing is overridden.

    在 3.13 版被加入.

  • -X presite=package.module specifies a module that should be imported before the site module is executed and before the __main__ module exists. Therefore, the imported module isn't __main__. This can be used to execute code early during Python initialization. Python needs to be built in debug mode for this option to exist. See also PYTHON_PRESITE.

    在 3.13 版被加入.

  • -X gil=0,1 forces the GIL to be disabled or enabled, respectively. Setting to 0 is only available in builds configured with --disable-gil. See also PYTHON_GIL and Free-threaded CPython.

    在 3.13 版被加入.

  • -X thread_inherit_context=0,1 causes Thread to, by default, use a copy of context of the caller of Thread.start() when starting. Otherwise, threads will start with an empty context. If unset, the value of this option defaults to 1 on free-threaded builds and to 0 otherwise. See also PYTHON_THREAD_INHERIT_CONTEXT.

    在 3.14 版被加入.

  • -X context_aware_warnings=0,1 causes the warnings.catch_warnings context manager to use a ContextVar to store warnings filter state. If unset, the value of this option defaults to 1 on free-threaded builds and to 0 otherwise. See also PYTHON_CONTEXT_AWARE_WARNINGS.

    在 3.14 版被加入.

  • -X tlbc=0,1 enables (1, the default) or disables (0) thread-local bytecode in builds configured with --disable-gil. When disabled, this also disables the specializing interpreter. See also PYTHON_TLBC.

    在 3.14 版被加入.

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

在 3.2 版被加入.

在 3.9 版的變更: 移除 -X showalloccount 選項。

在 3.10 版的變更: 移除 -X oldparser 選項。

在 3.14 版被移除: -J is no longer reserved for use by Jython, and now has no special meaning.

1.1.4. Controlling color

The Python interpreter is configured by default to use colors to highlight output in certain situations such as when displaying tracebacks. This behavior can be controlled by setting different environment variables.

Setting the environment variable TERM to dumb will disable color.

If the FORCE_COLOR environment variable is set, then color will be enabled regardless of the value of TERM. This is useful on CI systems which aren’t terminals but can still display ANSI escape sequences.

If the NO_COLOR environment variable is set, Python will disable all color in the output. This takes precedence over FORCE_COLOR.

All these environment variables are used also by other tools to control color output. To control the color output only in the Python interpreter, the PYTHON_COLORS environment variable can be used. This variable takes precedence over NO_COLOR, which in turn takes precedence over FORCE_COLOR.

1.2. 環境變數

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 介面選項. The search path can be manipulated from within a Python program as the variable sys.path.

PYTHONSAFEPATH

If this is set to a non-empty string, don't prepend a potentially unsafe path to sys.path: see the -P option for details.

在 3.11 版被加入.

PYTHONPLATLIBDIR

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

在 3.9 版被加入.

PYTHONSTARTUP