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
   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). 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*(*n*^2)
   complexity.  See http://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/python*version*" and
   "*exec_prefix*/lib/python*version*", 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/python*version*" (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

   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.

   引發一個附帶呼叫啟動時的檔案名稱為引數的稽核事件
   "cpython.run_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.

   在 3.7 版被加入.

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.

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

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.

   引發一個不附帶引數的稽核事件 "cpython.run_stdin"。

   在 3.12.5 版的變更: (also 3.11.10, 3.10.15, 3.9.20, and 3.8.20)
   Emits audit events.

   在 3.13 版的變更: Uses PyREPL if possible, in which case
   "PYTHONSTARTUP" is also executed. Emits audit events.

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 macOS.

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.

   在 3.8 版被加入.

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.

   在 3.2.3 版被加入.

PYTHONINTMAXSTRDIGITS

   If this variable is set to an integer, it is used to configure the
   interpreter's global integer string conversion length limitation.

   在 3.11 版被加入.

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'".

   在 3.4 版的變更: The "encodingname" part is now optional.

   在 3.6 版的變更: 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".

   也參考: **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 installation paths
   for "python -m pip install --user".

   也參考: **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 macOS.

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=all      # Same as PYTHONWARNINGS=always
      PYTHONWARNINGS=module   # Warn once per calling module
      PYTHONWARNINGS=once     # Warn once per Python process
      PYTHONWARNINGS=ignore   # Never warn

   See 警告過濾器 and 描述警告過濾器 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.

   在 3.3 版被加入.

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()" function
   for more information. This is equivalent to setting the "-X"
   "tracemalloc" option.

   在 3.4 版被加入.

PYTHONPROFILEIMPORTTIME

   If this environment variable is set to "1", Python will show how
   long each import takes. If set to "2", Python will include output
   for imported modules that have already been loaded. This is
   equivalent to setting the "-X" "importtime" option.

   在 3.7 版被加入.

   在 3.14 版的變更: Added "PYTHONPROFILEIMPORTTIME=2" to also trace
   imports of loaded modules.

PYTHONASYNCIODEBUG

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

   在 3.4 版被加入.

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.

   * "mimalloc": use the mimalloc 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.

   * "mimalloc_debug": same as "mimalloc" but also install debug
     hooks.

   在 3.6 版被加入.

   在 3.7 版的變更: Added the ""default"" allocator.

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.

   在 3.6 版的變更: 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
   error handler* 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()".

   可用性: Windows.

   在 3.6 版被加入: 更多細節請見 **PEP 529**。

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.

   可用性: Windows.

   在 3.6 版被加入.

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.

   可用性: Unix.

   在 3.7 版被加入: 更多細節請見 **PEP 538**。

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. This is equivalent to
   setting the "-X" "dev" option.

   在 3.7 版被加入.

PYTHONUTF8

   如果設為 "1"，則啟用 Python UTF-8 Mode。

   如果設為 "0"，則停用 Python UTF-8 Mode。

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

   在 3.7 版被加入.

PYTHONWARNDEFAULTENCODING

   If this environment variable is set to a non-empty string, issue a
   "EncodingWarning" when the locale-specific default encoding is
   used.

   細節請見 選擇性加入的編碼警告。

   在 3.10 版被加入.

PYTHONNODEBUGRANGES

   If this variable is set, it 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.

   在 3.11 版被加入.

PYTHONPERFSUPPORT

   If this variable is set to a nonzero value, it enables support for
   the Linux "perf" profiler so Python calls can be detected by it.

   If set to "0", disable Linux "perf" profiler support.

   See also the "-X perf" command-line option and Python 對 Linux perf
   分析器的支援.

   在 3.12 版被加入.

PYTHON_PERF_JIT_SUPPORT

   If this variable is set to a nonzero value, it enables support for
   the Linux "perf" profiler so Python calls can be detected by it
   using DWARF information.

   If set to "0", disable Linux "perf" profiler support.

   See also the "-X perf_jit" command-line option and Python 對 Linux
   perf 分析器的支援.

   在 3.13 版被加入.

PYTHON_DISABLE_REMOTE_DEBUG

   If this variable is set to a non-empty string, it disables the
   remote debugging feature 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.

   另請參閱 "-X disable_remote_debug" 命令列選項。

   在 3.14 版被加入.

PYTHON_CPU_COUNT

   If this variable is set to a positive integer, it overrides the
   return values of "os.cpu_count()" and "os.process_cpu_count()".

   另請參閱 "-X cpu_count" 命令列選項。

   在 3.13 版被加入.

PYTHON_FROZEN_MODULES

   If this variable is set to "on" or "off", it 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" for non-debug builds (the normal case) and "off"
   for debug builds. Note that the "importlib_bootstrap" and
   "importlib_bootstrap_external" frozen modules are always used, even
   if this flag is set to "off".

   另請參閱 "-X frozen_modules" 命令列選項。

   在 3.13 版被加入.

PYTHON_COLORS

   If this variable is set to "1", the interpreter will colorize
   various kinds of output. Setting it to "0" deactivates this
   behavior. See also Controlling color.

   在 3.13 版被加入.

PYTHON_BASIC_REPL

   If this variable is set to any value, the interpreter will not
   attempt to load the Python-based *REPL* that requires "readline",
   and will instead use the traditional parser-based *REPL*.

   在 3.13 版被加入.

PYTHON_HISTORY

   This environment variable can be used to set the location of a
   ".python_history" file (by default, it is ".python_history" in the
   user's home directory).

   在 3.13 版被加入.

PYTHON_GIL

   If this variable is set to "1", the global interpreter lock (GIL)
   will be forced on. Setting it to "0" forces the GIL off (needs
   Python configured with the "--disable-gil" build option).

   See also the "-X gil" command-line option, which takes precedence
   over this variable, and Free-threaded CPython.

   在 3.13 版被加入.

PYTHON_THREAD_INHERIT_CONTEXT

   If this variable is set to "1" then "Thread" will, by default, use
   a copy of context of the caller of "Thread.start()" when starting.
   Otherwise, new threads will start with an empty context. If unset,
   this variable defaults to "1" on free-threaded builds and to "0"
   otherwise.  See also "-X thread_inherit_context".

   在 3.14 版被加入.

PYTHON_CONTEXT_AWARE_WARNINGS

   If set to "1" then the "warnings.catch_warnings" context manager
   will use a "ContextVar" to store warnings filter state.  If unset,
   this variable defaults to "1" on free-threaded builds and to "0"
   otherwise.  See "-X context_aware_warnings".

   在 3.14 版被加入.

PYTHON_JIT

   On builds where experimental just-in-time compilation is available,
   this variable can force the JIT to be disabled ("0") or enabled
   ("1") at interpreter startup.

   在 3.13 版被加入.

PYTHON_TLBC

   If set to "1" enables thread-local bytecode. If set to "0" thread-
   local bytecode and the specializing interpreter are disabled.  Only
   applies to builds configured with "--disable-gil".

   另請參閱 "-X tlbc" 命令列選項。

   在 3.14 版被加入.


1.2.1. 除錯模式變數
-------------------

PYTHONDUMPREFS

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

   Needs Python configured with the "--with-trace-refs" build option.

PYTHONDUMPREFSFILE

   If set, Python will dump objects and reference counts still alive
   after shutting down the interpreter into a file under the path
   given as the value to this environment variable.

   Needs Python configured with the "--with-trace-refs" build option.

   在 3.11 版被加入.

PYTHON_PRESITE

   If this variable is set to a module, that module will be imported
   early in the interpreter lifecycle, before the "site" module is
   executed, and before the "__main__" module is created. Therefore,
   the imported module is not treated as "__main__".

   This can be used to execute code early during Python
   initialization.

   To import a submodule, use "package.module" as the value, like in
   an import statement.

   See also the "-X presite" command-line option, which takes
   precedence over this variable.

   Needs Python configured with the "--with-pydebug" build option.

   在 3.13 版被加入.
