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。
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
The interpreter interface resembles that of the UNIX shell, but provides some additional methods of invocation:
Ctrl-D
on UNIX or
Ctrl-Z, Enter
on Windows) is read.
-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!
-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)。
-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
)。
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 (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
.
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()
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
<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。
另请参阅
runpy.run_path()
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
3.4 版改变： 自动启用 Tab 补全和历史编辑。
-b
Issue a warning when comparing str and bytes. Issue an error when the option is given twice (
-bb
).
-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
.
-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。
-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
Turn on basic optimizations. This changes the filename extension for compiled (
bytecode
) files from
.pyc
to
.pyo
。另请参阅
PYTHONOPTIMIZE
.
-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
Kept for compatibility. On Python 3.3 and greater, hash randomization is turned on by default.
On previous versions of Python, this option turns on hash randomization, so that the
__hash__()
values of str, bytes and datetime 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。
3.2.3 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
Force the binary layer of the stdout and stderr streams (which is available as their
buffer
attribute) to be unbuffered. The text I/O layer will still be line-buffered if writing to the console, or block-buffered if redirected to a non-interactive file.
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.
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 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):
ignore
default
all
module
once
error
The full form of argument is:
action:message:category:module:line
这里， 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 module 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
-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.
-X
Reserved for various implementation-specific options. CPython currently defines the following possible values:
-X faulthandler
以启用
faulthandler
;
-X showrefcount
to enable the output of the total reference count
and memory blocks (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。
It also allows to pass arbitrary values and retrieve them through the
sys._xoptions
字典。
3.2 版改变：
It is now allowed to pass
-X
with CPython.
3.3 版新增：
The
-X faulthandler
选项。
3.4 版新增：
The
-X showrefcount
and
-X tracemalloc
选项。
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.
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。
PYTHONDONTWRITEBYTECODE
¶
If this is set to a non-empty string, 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。
PYTHONHASHSEED
¶
若此变量未设置或被设为
random
, a random value is used to seed the hashes of str, bytes and datetime 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。
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
多次。
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。
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
¶
若设置，Python 将打印线程调试信息。
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。
PYTHONMALLOCSTATS
¶
If set, Python will print memory allocation statistics every time a new object arena is created, and on shutdown.