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 [-BdEiOQsRStuUvVWxX3?] [-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.
  • 当调用采用 -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!
  • 当调用采用 -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 command . command 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)。

-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 模块 name, you must not give a file extension ( .py ). The module-name should be a valid 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 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. As with the -c option, the current directory will be added to the start of sys.path .

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

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

另请参阅

runpy.run_module()
等效功能可直接用于 Python 代码

PEP 338 – Executing modules as scripts

2.4 版新增。

Changed in version 2.5: The named module can now be located inside a package.

2.7 版改变: 提供包名称以运行 __main__ submodule. sys.argv[0] is now set to "-m" while searching for the module (it was previously incorrectly set to "-c" )

-

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 .

<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 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__ 模块。

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

Changed in version 2.5: Directories and zipfiles containing a __main__.py file at the top level are now considered valid Python scripts.

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 .

另请参阅

援引解释器

1.1.2. 一般选项

- ?
-h
--help

打印所有命令行选项的简短描述。

Changed in version 2.5: --help variant.

-V
--version

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

Python 2.5.1
											

Changed in version 2.5: --version variant.

1.1.3. 杂项选项

-B

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

2.6 版新增。

-d

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

-E

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

2.2 版新增。

-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 .

-O

Turn on basic optimizations. This changes the filename extension for compiled ( bytecode ) files from .pyc to .pyo 。另请参阅 PYTHONOPTIMIZE .

-OO

Discard docstrings in addition to the -O optimizations.

-Q <arg>

Division control. The argument must be one of the following:

old
division of int/int and long/long return an int or long ( default )
new
new division semantics, i.e. division of int/int and long/long returns a float
warn
old division semantics with a warning for int/int and long/long
warnall
old division semantics with a warning for all uses of the division operator

另请参阅

Tools/scripts/fixdiv.py
for a use of warnall

PEP 238 – Changing the division operator

-R

Turn on hash randomization, so that the __hash__() values of str, bytes and datetime 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.

This 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。

Changing hash values affects the order in which keys are retrieved from a dict. Although Python has never made guarantees about this ordering (and it typically varies between 32-bit and 64-bit builds), enough real-world code implicitly relies on this non-guaranteed behavior that the randomization is disabled by default.

另请参阅 PYTHONHASHSEED .

New in version 2.6.8.

-s

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

2.6 版新增。

另请参阅

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.

-t

Issue a warning when a source file mixes tabs and spaces for indentation in a way that makes it depend on the worth of a tab expressed in spaces. Issue an error when the option is given twice ( -tt ).

-u

Force stdin, stdout and stderr to be totally unbuffered. On systems where it matters, also put stdin, stdout and stderr in binary mode.

Note that there is internal buffering in file.readlines() and 文件对象 ( for line in sys.stdin ) which is not influenced by this option. To work around this, you will want to use file.readline() inside a while 1: loop.

另请参阅 PYTHONUNBUFFERED .

-v

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

-W arg

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

file:line: category: message
											

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

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

Starting from Python 2.7, DeprecationWarning and its descendants are ignored by default. The -Wd option can be used to re-enable them.

Warnings can also be controlled from within a Python program using the warnings 模块。

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

ignore
忽略所有警告。
default
Explicitly request the default behavior (printing each warning once per source line).
all
Print a warning each time it occurs (this may generate many messages if a warning is triggered repeatedly for the same source line, such as inside a loop).
模块
Print each warning only the first time it occurs in each module.
once
Print each warning only the first time it occurs in the program.
error
Raise an exception instead of printing a warning message.

The full form of argument is:

action:message:category:module:line
											

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

另请参阅

warnings – the warnings module

PEP 230 – Warning framework

PYTHONWARNINGS

-x

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

注意

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

-3

Warn about Python 3.x possible incompatibilities by emitting a DeprecationWarning for features that are removed or significantly changed in Python 3.

2.6 版新增。

1.1.4. 不应该使用的选项

-J

Reserved for use by Jython .

-U

Turns all string literals into unicodes globally. Do not be tempted to use this option as it will probably break your world. It also produces .pyc files with a different magic number than normal. Instead, you can enable unicode literals on a per-module basis by using:

from __future__ import unicode_literals
											

at the top of the file. See __future__ 了解细节。

-X

Reserved for alternative implementations of Python to use for their own purposes.

1.2. 环境变量

These environment variables influence Python’s behavior, they are processed before the command-line switches other than -E. 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 ,其中 prefix and exec_prefix are installation-dependent directories, both defaulting to /usr/local .

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 (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 in this file.

PYTHONY2K

Set this to a non-empty string to cause the time module to require dates specified as strings to include 4-digit years, otherwise 2-digit years are converted based on rules described in the time 模块文档编制。

PYTHONOPTIMIZE

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

PYTHONDEBUG

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

PYTHONINSPECT

If this is set to a non-empty string it is equivalent to specifying the -i 选项。

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 选项。

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, OS X, OS/2, and RiscOS.

PYTHONDONTWRITEBYTECODE

If this is set, Python won’t try to write .pyc or .pyo files on the import of source modules. This is equivalent to specifying the -B 选项。

2.6 版新增。

PYTHONHASHSEED

If this variable is set to random , the effect is the same as specifying the -R option: a random value is used to seed the hashes of str, bytes and datetime objects.

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 lead to the same hash values as when hash randomization is disabled.

New in version 2.6.8.

PYTHONIOENCODING

Overrides the encoding used for stdin/stdout/stderr, in the syntax encodingname:errorhandler :errorhandler part is optional and has the same meaning as in str.encode() .

2.6 版新增。

PYTHONNOUSERSITE

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

2.6 版新增。

另请参阅

PEP 370 – Per user site-packages directory

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 安装 --user .

2.6 版新增。

另请参阅

PEP 370 – Per user site-packages directory

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.

1.2.1. 调试模式变量

Setting these variables only has an effect in a debug build of Python, that is, if Python was configured with the --with-pydebug 构建选项。

PYTHONTHREADDEBUG

If set, Python will print threading debug info.

2.6 版改变: Previously, this variable was called THREADDEBUG .

PYTHONDUMPREFS

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

PYTHONMALLOCSTATS

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