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1. 命令行和环境

CPython 解释器扫描命令行和各种设置的环境。

CPython 实现细节： 其它实现的命令行方案可能不同。见 替代实现 为进一步资源。

1.1. 命令行

当援引 Python 时，可以指定这些任何选项： 

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

当然，最常见用例是简单援引脚本： 

python myscript.py

1.1.1. 接口选项

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.

  • 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.

  • 当被调用采用 -c command , it executes the Python statement(s) given as 命令 . Here 命令 may contain multiple statements separated by newlines. Leading whitespace is significant in Python statements!

  • 当被调用采用 -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>

执行 Python 代码在 命令 . 命令 可以是由换行符分隔的一条或多条语句，采用如正常模块代码中的显著前导空格。

若给出此选项，第一元素对于 sys.argv 将是 "-c" 且当前目录将被添加到起始在 sys.path (允许该目录下的模块被导入作为顶层模块)。

引发 审计事件 cpython.run_command 采用自变量 command .

-m <module-name>

搜索 sys.path for the named module and execute its contents as the __main__ 模块。

由于自变量是 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.

注意

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.

若给出此选项，第一元素对于 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 模块： 

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

引发 审计事件 cpython.run_module 采用自变量 module-name .

另请参阅

runpy.run_module()

等效功能可直接用于 Python 代码

PEP 338 – 将模块作为脚本执行

3.1 版改变： 提供包名称以运行 __main__ 子模块。

3.4 版改变： 还支持名称空间包

-

读取命令从标准输入 ( sys.stdin )。若标准输入是终端， -i 是隐含的。

若给出此选项，第一元素对于 sys.argv 将是 "-" 且当前目录将被添加到起始在 sys.path .

引发 审计事件 cpython.run_stdin 不带自变量。

<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 文件。

若给出此选项，第一元素对于 sys.argv 将是作为在命令行给出的脚本名称。

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__ 模块。

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

-I option can be used to run the script in isolated mode where sys.path 既不包含脚本目录，也不包含用户站点包目录。所有 PYTHON* environment variables are ignored, too.

引发 审计事件 cpython.run_file 采用自变量 filename .

另请参阅

runpy.run_path()

等效功能可直接用于 Python 代码

若未给出接口选项， -i 是隐含的， sys.argv[0] 为空字符串 ( "" ) 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 配置 ).

另请参阅

援引解释器

3.4 版改变： 自动启用 Tab 补全和历史编辑。

1.1.2. 一般选项

-?
-h
--help

打印所有命令行选项的简短描述。

-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]

3.6 版新增： The -VV 选项。

1.1.3. 杂项选项

-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 ).

3.5 版改变： Affects comparisons of bytes with int .

-B

若给定，Python 不会试着写入 .pyc 文件当导入源模块时。另请参阅 PYTHONDONTWRITEBYTECODE .

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

Control the validation behavior of hash-based .pyc 文件。见 缓存字节码无效 。当设为 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

打开剖析器调试输出 (仅针对专家，从属编译选项)。另请参阅 PYTHONDEBUG .

-E

忽略所有 PYTHON* 环境变量，如 PYTHONPATH and PYTHONHOME ，可能有设置。

-i

当传递脚本作为第一自变量或 -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 既不包含脚本目录，也不包含用户站点包目录。所有 PYTHON* 环境变量也被忽略。可以施加进一步限定以阻止用户注入恶意代码。

3.4 版新增。

-O

移除 assert 语句和任何代码，若代码条件值为 __debug__ 。filename 自变量用于编译 ( bytecode ) 文件通过添加 .opt-1 先于 .pyc 扩展 (见 PEP 488 )。另请参阅 PYTHONOPTIMIZE .

3.5 版改变： 修改 .pyc 文件名根据 PEP 488 .

-OO

Do -O 且还会丢弃 docstring (文档字符串)。filename 自变量用于编译 ( bytecode ) 文件通过添加 .opt-2 先于 .pyc 扩展 (见 PEP 488 ).

3.5 版改变： 修改 .pyc 文件名根据 PEP 488 .

-q

不显示版权和版本消息，即使在交互模式下。

3.2 版新增。

-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 了解细节。

PYTHONHASHSEED 允许为哈希种子保密设置固定值。

3.7 版改变： 选项不再被忽略。

3.2.3 版新增。

-s

不添加 user site-packages directory to sys.path .

另请参阅

PEP 370 – 每用户站点包目录

-S

禁用导入模块 site 和从属站点操纵 sys.path 牵涉的。还禁用这些操纵若 site 稍后被明确导入 (调用 site.main() 若想要触发它们)。

-u

强制 stdout 和 stderr 流无缓冲。此选项不影响 stdin 流。

另请参阅 PYTHONUNBUFFERED .

3.7 版改变： stdout 和 stderr 流的文本层现在是无缓冲的。

-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.

多 -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 using the PYTHONWARNINGS environment variable and from within a Python program using the warnings 模块。

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
-Wmodule   # Warn once per calling module
-Wonce     # Warn once per Python process
-Wignore   # Never warn

The action names can be abbreviated as desired (e.g. -Wi , -Wd , -Wa , -We ) and the interpreter will resolve them to the appropriate action name.

见 警告过滤 and 描述警告过滤 了解更多细节。

-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 以启用 faulthandler ;

  • -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.

  • -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() 了解更多信息。

  • -X showalloccount to output the total count of allocated objects for each type when the program finishes. This only works when Python was built with COUNT_ALLOCS defined.

  • -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 python3 -X importtime -c 'import asyncio' 。另请参阅 PYTHONPROFILEIMPORTTIME .

  • -X dev : enable CPython’s “development mode”, introducing additional runtime checks which are too expensive to be enabled by default. It should not be more verbose than the default if the code is correct: new warnings are only emitted when an issue is detected. Effect of the developer mode:

  • -X utf8 为操作系统接口启用 UTF-8 模式，覆盖默认区域设置感知模式。 -X utf8=0 明确禁用 UTF-8 模式 (甚至在它被自动激活时)。见 PYTHONUTF8 了解更多细节。

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

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

3.2 版改变： The -X 选项被添加。

3.3 版新增： The -X faulthandler 选项。

3.4 版新增： The -X showrefcount and -X tracemalloc 选项。

3.6 版新增： The -X showalloccount 选项。

3.7 版新增： The -X importtime , -X dev and -X utf8 选项。

3.8 版新增： The -X pycache_prefix 选项。 -X dev 选项现在日志 close() 异常在 io.IOBase 析构函数。

1.1.4. 不应使用的选项

-J

预留为用于 Jython .

1.2. 环境变量

这些环境变量影响 Python 行为，它们的处理是在命令行开关前，而不是 -E 或 -I。习惯上，命令行开关覆写有冲突地方的环境变量。

PYTHONHOME

更改标准 Python 库的位置。默认情况下，库的搜索是在 prefix/lib/pythonversion and exec_prefix/lib/pythonversion ，其中 prefix and exec_prefix 安装依赖目录，两者默认为 /usr/local .

当 PYTHONHOME 被设为单目录，它的值替换 prefix and exec_prefix 。要为这些指定不同值，设置 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 (见 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 接口选项 . 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.

引发 审计事件 cpython.run_startup with the filename as the argument when called on startup.

PYTHONOPTIMIZE

若将这设为非空字符串，相当于指定 -O 选项。若设为整数，相当于指定 -O 多次。

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.

3.7 版新增。

PYTHONDEBUG

若将这设为非空字符串，相当于指定 -d 选项。若设为整数，相当于指定 -d 多次。

PYTHONINSPECT

若将这设为非空字符串，相当于指定 -i 选项。

此变量也可以被修改通过 Python 代码使用 os.environ 以强制审查模式，当程序终止时。

PYTHONUNBUFFERED

若将这设为非空字符串，相当于指定 -u 选项。

PYTHONVERBOSE

若将这设为非空字符串，相当于指定 -v 选项。若设为整数，相当于指定 -v 多次。

PYTHONCASEOK

若设置这，Python 忽略大小写在 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 选项。

PYTHONPYCACHEPREFIX

若设置这，Python 将写入 .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 选项。

3.8 版新增。

PYTHONHASHSEED

若此变量未设置或被设为 random , a random value is used to seed the hashes of str and bytes objects.

若 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.

3.2.3 版新增。

PYTHONIOENCODING

若在运行解释器之前设置，这会覆盖用于 stdin/stdout/stderr 的编码，按句法 encodingname:errorhandler 。两者 encodingname 和 :errorhandler 部件是可选的，且拥有相同含义如在 str.encode() .

对于 stderr， :errorhandler 部分被忽略；处理程序将始终为 'backslashreplace' .

3.4 版改变： The encodingname 部分现在是可选的。

3.6 版改变： 在 Windows，交互控制台缓冲忽略由此变量指定的编码，除非 PYTHONLEGACYWINDOWSSTDIO 也有指定。透过标准流重定向的文件和管道不受影响。

PYTHONNOUSERSITE

若设置这，Python 将不添加 user site-packages directory to sys.path .

另请参阅

PEP 370 – 每用户站点包目录

PYTHONUSERBASE

定义 user base directory , which is used to compute the path of the user site-packages directory and distutils 安装路径 for python setup.py install --user .

另请参阅

PEP 370 – 每用户站点包目录

PYTHONEXECUTABLE

若此环境变量有设置， 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

这相当于 -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

见 警告过滤 and 描述警告过滤 了解更多细节。

PYTHONFAULTHANDLER

若此环境变量被设为非空字符串， faulthandler.enable() 被调用在启动时：安装处理程序为 SIGSEGV , SIGFPE , SIGABRT , SIGBUS and SIGILL 信号以转储 Python 回溯。这相当于 -X faulthandler 选项。

3.3 版新增。

PYTHONTRACEMALLOC

若此环境变量被设为非空字符串，开始跟踪 Python 内存分配使用 tracemalloc 模块。变量的值是存储在跟踪回溯中的最大帧数。例如， PYTHONTRACEMALLOC=1 仅存储最近帧。见 tracemalloc.start() 了解更多信息。

3.4 版新增。

PYTHONPROFILEIMPORTTIME

若此环境变量被设为非空字符串，Python 将展示每次导入花费的时间。这准确相当于设置 -X importtime 在命令行。

3.7 版新增。

PYTHONASYNCIODEBUG

若此环境变量被设为非空字符串，启用 调试模式 的 asyncio 模块。

3.4 版新增。

PYTHONMALLOC

设置 Python 内存分配器和/或安装调试挂钩。

设置 Python 使用的内存分配器系列：

安装调试挂钩：

  • debug ：将调试挂钩安装在顶部为 默认内存分配器 .

  • malloc_debug ：如同 malloc 但还安装调试挂钩。

  • pymalloc_debug ：如同 pymalloc 但还安装调试挂钩。

见 默认内存分配器 和 PyMem_SetupDebugHooks() 函数 (在 Python 内存分配器中安装调试挂钩)。

3.7 版改变： 添加 "default" 分配器。

3.6 版新增。

PYTHONMALLOCSTATS

If set to a non-empty string, Python will print statistics of the pymalloc 内存分配器 每次创建新 pymalloc 对象 arena 时和关闭时。

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 支持。

3.6 版改变： 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.

这也可以在运行时被启用采用 sys._enablelegacywindowsfsencoding() .

可用性 ：Windows。

3.6 版新增： 见 PEP 529 了解更多细节。

PYTHONLEGACYWINDOWSSTDIO

若设为非空字符串，不使用新的控制台读取器和写入器。这意味着 Unicode 字符将根据活动控制台代码页编码，而不是使用 UTF-8。

此变量被忽略，若标准流被重定向 (到文件或管道) 而不是引用控制台缓冲。

可用性 ：Windows。

3.6 版新增。

PYTHONCOERCECLOCALE

若设为值 0 ，导致主 Python 命令行应用程序跳过将传统基于 ASCII 的 C 和 POSIX 区域设置强制转换为能力更强基于 UTF-8 的替代。

若此变量 not set (or is set to a value other than 0 )， 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 错误处理程序 for sys.stdin and sys.stdout ( sys.stderr 继续使用 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 而不是 UTF-8 for system interfaces.

可用性 : *nix.

3.7 版新增： 见 PEP 538 了解更多细节。

PYTHONDEVMODE

If this environment variable is set to a non-empty string, enable the CPython “development mode”. See the -X dev 选项。

3.7 版新增。

PYTHONUTF8

若设为 1 ，启用解释器的 UTF-8 模式，其中 UTF-8 被用作系统接口的文本编码，不管当前区域设置。

这意味着：

因此，改变这些更低级的 API，其它更高级 API 还会显露不同默认行为：

  • 使用 UTF-8 编码将命令行自变量，环境变量及文件名解码成文本。

  • os.fsdecode() and os.fsencode() 使用 UTF-8 编码。

  • open() , io.open() ，和 codecs.open() 默认使用 UTF-8 编码。不管怎样，它们默认仍使用严格错误处理程序，所以试图以文本模式打开二进制文件可能引发异常而不是产生无感觉数据。

注意，可以按 UTF-8 模式覆盖标准流设置通过 PYTHONIOENCODING (就像它们可以在默认区域设置感知模式下)。

若设为 0 ，解释器运行在其默认区域设置感知模式下。

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.

也可用作 -X utf8 选项。

3.7 版新增： 见 PEP 540 了解更多细节。

1.2.1. 调试模式变量

设置这些变量才有效当调试 Python 构建时。

PYTHONTHREADDEBUG

若设置，Python 将打印线程调试信息。

需要配置 Python 采用 --with-pydebug 构建选项。

PYTHONDUMPREFS

若设置，Python 将转储仍然存活的对象和引用计数在关闭解释器之后。

需要配置 Python 采用 --with-trace-refs 构建选项。

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