642 lines
21 KiB
ReStructuredText
642 lines
21 KiB
ReStructuredText
.. highlightlang:: sh
|
|
|
|
.. ATTENTION: You probably should update Misc/python.man, too, if you modify
|
|
this file.
|
|
|
|
.. _using-on-general:
|
|
|
|
Command line and environment
|
|
============================
|
|
|
|
The CPython interpreter scans the command line and the environment for various
|
|
settings.
|
|
|
|
.. impl-detail::
|
|
|
|
Other implementations' command line schemes may differ. See
|
|
:ref:`implementations` for further resources.
|
|
|
|
|
|
.. _using-on-cmdline:
|
|
|
|
Command line
|
|
------------
|
|
|
|
When invoking Python, you may specify any of these options::
|
|
|
|
python [-bBdEhiIOqsSuvVWx?] [-c command | -m module-name | script | - ] [args]
|
|
|
|
The most common use case is, of course, a simple invocation of a script::
|
|
|
|
python myscript.py
|
|
|
|
|
|
.. _using-on-interface-options:
|
|
|
|
Interface options
|
|
~~~~~~~~~~~~~~~~~
|
|
|
|
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 :kbd:`Ctrl-D` on UNIX or :kbd:`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.
|
|
* 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 :data:`sys.argv` -- note that the first
|
|
element, subscript zero (``sys.argv[0]``), is a string reflecting the program's
|
|
source.
|
|
|
|
.. cmdoption:: -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 :data:`sys.argv` will be
|
|
``"-c"`` and the current directory will be added to the start of
|
|
:data:`sys.path` (allowing modules in that directory to be imported as top
|
|
level modules).
|
|
|
|
|
|
.. cmdoption:: -m <module-name>
|
|
|
|
Search :data:`sys.path` for the named module and execute its contents as
|
|
the :mod:`__main__` module.
|
|
|
|
Since the argument is a *module* 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 (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.
|
|
|
|
.. note::
|
|
|
|
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 :data:`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 :option:`-c` option,
|
|
the current directory will be added to the start of :data:`sys.path`.
|
|
|
|
Many standard library modules contain code that is invoked on their execution
|
|
as a script. An example is the :mod:`timeit` module::
|
|
|
|
python -mtimeit -s 'setup here' 'benchmarked code here'
|
|
python -mtimeit -h # for details
|
|
|
|
.. seealso::
|
|
:func:`runpy.run_module`
|
|
Equivalent functionality directly available to Python code
|
|
|
|
:pep:`338` -- Executing modules as scripts
|
|
|
|
|
|
.. versionchanged:: 3.1
|
|
Supply the package name to run a ``__main__`` submodule.
|
|
|
|
.. versionchanged:: 3.4
|
|
namespace packages are also supported
|
|
|
|
|
|
.. describe:: -
|
|
|
|
Read commands from standard input (:data:`sys.stdin`). If standard input is
|
|
a terminal, :option:`-i` is implied.
|
|
|
|
If this option is given, the first element of :data:`sys.argv` will be
|
|
``"-"`` and the current directory will be added to the start of
|
|
:data:`sys.path`.
|
|
|
|
|
|
.. describe:: <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 :data:`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 :data:`sys.path`, and the
|
|
file is executed as the :mod:`__main__` module.
|
|
|
|
If the script name refers to a directory or zipfile, the script name is
|
|
added to the start of :data:`sys.path` and the ``__main__.py`` file in
|
|
that location is executed as the :mod:`__main__` module.
|
|
|
|
.. seealso::
|
|
:func:`runpy.run_path`
|
|
Equivalent functionality directly available to Python code
|
|
|
|
|
|
If no interface option is given, :option:`-i` is implied, ``sys.argv[0]`` is
|
|
an empty string (``""``) and the current directory will be added to the
|
|
start of :data:`sys.path`. Also, tab-completion and history editing is
|
|
automatically enabled, if available on your platform (see
|
|
:ref:`rlcompleter-config`).
|
|
|
|
.. seealso:: :ref:`tut-invoking`
|
|
|
|
.. versionchanged:: 3.4
|
|
Automatic enabling of tab-completion and history editing.
|
|
|
|
|
|
Generic options
|
|
~~~~~~~~~~~~~~~
|
|
|
|
.. cmdoption:: -?
|
|
-h
|
|
--help
|
|
|
|
Print a short description of all command line options.
|
|
|
|
|
|
.. cmdoption:: -V
|
|
--version
|
|
|
|
Print the Python version number and exit. Example output could be::
|
|
|
|
Python 3.0
|
|
|
|
|
|
.. _using-on-misc-options:
|
|
|
|
Miscellaneous options
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. cmdoption:: -b
|
|
|
|
Issue a warning when comparing str and bytes. Issue an error when the
|
|
option is given twice (:option:`-bb`).
|
|
|
|
|
|
.. cmdoption:: -B
|
|
|
|
If given, Python won't try to write ``.pyc`` or ``.pyo`` files on the
|
|
import of source modules. See also :envvar:`PYTHONDONTWRITEBYTECODE`.
|
|
|
|
|
|
.. cmdoption:: -d
|
|
|
|
Turn on parser debugging output (for wizards only, depending on compilation
|
|
options). See also :envvar:`PYTHONDEBUG`.
|
|
|
|
|
|
.. cmdoption:: -E
|
|
|
|
Ignore all :envvar:`PYTHON*` environment variables, e.g.
|
|
:envvar:`PYTHONPATH` and :envvar:`PYTHONHOME`, that might be set.
|
|
|
|
|
|
.. cmdoption:: -i
|
|
|
|
When a script is passed as first argument or the :option:`-c` option is used,
|
|
enter interactive mode after executing the script or the command, even when
|
|
:data:`sys.stdin` does not appear to be a terminal. The
|
|
:envvar:`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 :envvar:`PYTHONINSPECT`.
|
|
|
|
|
|
.. cmdoption:: -I
|
|
|
|
Run Python in isolated mode. This also implies -E and -s.
|
|
In isolated mode :data:`sys.path` contains neither the script's directory nor
|
|
the user's site-packages directory. All :envvar:`PYTHON*` environment
|
|
variables are ignored, too. Further restrictions may be imposed to prevent
|
|
the user from injecting malicious code.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
.. cmdoption:: -O
|
|
|
|
Turn on basic optimizations. This changes the filename extension for
|
|
compiled (:term:`bytecode`) files from ``.pyc`` to ``.pyo``. See also
|
|
:envvar:`PYTHONOPTIMIZE`.
|
|
|
|
|
|
.. cmdoption:: -OO
|
|
|
|
Discard docstrings in addition to the :option:`-O` optimizations.
|
|
|
|
|
|
.. cmdoption:: -q
|
|
|
|
Don't display the copyright and version messages even in interactive mode.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. cmdoption:: -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 :meth:`__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 for details.
|
|
|
|
:envvar:`PYTHONHASHSEED` allows you to set a fixed value for the hash
|
|
seed secret.
|
|
|
|
.. versionadded:: 3.2.3
|
|
|
|
|
|
.. cmdoption:: -s
|
|
|
|
Don't add the :data:`user site-packages directory <site.USER_SITE>` to
|
|
:data:`sys.path`.
|
|
|
|
.. seealso::
|
|
|
|
:pep:`370` -- Per user site-packages directory
|
|
|
|
|
|
.. cmdoption:: -S
|
|
|
|
Disable the import of the module :mod:`site` and the site-dependent
|
|
manipulations of :data:`sys.path` that it entails. Also disable these
|
|
manipulations if :mod:`site` is explicitly imported later (call
|
|
:func:`site.main` if you want them to be triggered).
|
|
|
|
|
|
.. cmdoption:: -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.
|
|
|
|
See also :envvar:`PYTHONUNBUFFERED`.
|
|
|
|
|
|
.. cmdoption:: -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
|
|
(:option:`-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 :envvar:`PYTHONVERBOSE`.
|
|
|
|
|
|
.. cmdoption:: -W arg
|
|
|
|
Warning control. Python's warning machinery by default prints warning
|
|
messages to :data:`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 :option:`-W` options may be given; when a warning matches more than
|
|
one option, the action for the last matching option is performed. Invalid
|
|
:option:`-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
|
|
:mod:`warnings` module.
|
|
|
|
The simplest form of argument is one of the following action strings (or a
|
|
unique abbreviation):
|
|
|
|
``ignore``
|
|
Ignore all warnings.
|
|
``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).
|
|
``module``
|
|
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 *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.
|
|
|
|
.. seealso::
|
|
:mod:`warnings` -- the warnings module
|
|
|
|
:pep:`230` -- Warning framework
|
|
|
|
:envvar:`PYTHONWARNINGS`
|
|
|
|
|
|
.. cmdoption:: -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.
|
|
|
|
.. note:: The line numbers in error messages will be off by one.
|
|
|
|
|
|
.. cmdoption:: -X
|
|
|
|
Reserved for various implementation-specific options. CPython currently
|
|
defines the following possible values:
|
|
|
|
* ``-X faulthandler`` to enable :mod:`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
|
|
:mod:`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
|
|
:func:`tracemalloc.start` for more information.
|
|
|
|
It also allows to pass arbitrary values and retrieve them through the
|
|
:data:`sys._xoptions` dictionary.
|
|
|
|
.. versionchanged:: 3.2
|
|
It is now allowed to pass :option:`-X` with CPython.
|
|
|
|
.. versionadded:: 3.3
|
|
The ``-X faulthandler`` option.
|
|
|
|
.. versionadded:: 3.4
|
|
The ``-X showrefcount`` and ``-X tracemalloc`` options.
|
|
|
|
|
|
Options you shouldn't use
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. cmdoption:: -J
|
|
|
|
Reserved for use by Jython_.
|
|
|
|
.. _Jython: http://www.jython.org/
|
|
|
|
|
|
.. _using-on-envvars:
|
|
|
|
Environment variables
|
|
---------------------
|
|
|
|
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.
|
|
|
|
.. envvar:: PYTHONHOME
|
|
|
|
Change the location of the standard Python libraries. By default, the
|
|
libraries are searched in :file:`{prefix}/lib/python{version}` and
|
|
:file:`{exec_prefix}/lib/python{version}`, where :file:`{prefix}` and
|
|
:file:`{exec_prefix}` are installation-dependent directories, both defaulting
|
|
to :file:`/usr/local`.
|
|
|
|
When :envvar:`PYTHONHOME` is set to a single directory, its value replaces
|
|
both :file:`{prefix}` and :file:`{exec_prefix}`. To specify different values
|
|
for these, set :envvar:`PYTHONHOME` to :file:`{prefix}:{exec_prefix}`.
|
|
|
|
|
|
.. envvar:: PYTHONPATH
|
|
|
|
Augment the default search path for module files. The format is the same as
|
|
the shell's :envvar:`PATH`: one or more directory pathnames separated by
|
|
:data:`os.pathsep` (e.g. colons on Unix or semicolons on Windows).
|
|
Non-existent directories are silently ignored.
|
|
|
|
In addition to normal directories, individual :envvar:`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
|
|
:file:`{prefix}/lib/python{version}` (see :envvar:`PYTHONHOME` above). It
|
|
is *always* appended to :envvar:`PYTHONPATH`.
|
|
|
|
An additional directory will be inserted in the search path in front of
|
|
:envvar:`PYTHONPATH` as described above under
|
|
:ref:`using-on-interface-options`. The search path can be manipulated from
|
|
within a Python program as the variable :data:`sys.path`.
|
|
|
|
|
|
.. envvar:: 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 :data:`sys.ps1` and
|
|
:data:`sys.ps2` and the hook :data:`sys.__interactivehook__` in this file.
|
|
|
|
|
|
.. envvar:: PYTHONOPTIMIZE
|
|
|
|
If this is set to a non-empty string it is equivalent to specifying the
|
|
:option:`-O` option. If set to an integer, it is equivalent to specifying
|
|
:option:`-O` multiple times.
|
|
|
|
|
|
.. envvar:: PYTHONDEBUG
|
|
|
|
If this is set to a non-empty string it is equivalent to specifying the
|
|
:option:`-d` option. If set to an integer, it is equivalent to specifying
|
|
:option:`-d` multiple times.
|
|
|
|
|
|
.. envvar:: PYTHONINSPECT
|
|
|
|
If this is set to a non-empty string it is equivalent to specifying the
|
|
:option:`-i` option.
|
|
|
|
This variable can also be modified by Python code using :data:`os.environ`
|
|
to force inspect mode on program termination.
|
|
|
|
|
|
.. envvar:: PYTHONUNBUFFERED
|
|
|
|
If this is set to a non-empty string it is equivalent to specifying the
|
|
:option:`-u` option.
|
|
|
|
|
|
.. envvar:: PYTHONVERBOSE
|
|
|
|
If this is set to a non-empty string it is equivalent to specifying the
|
|
:option:`-v` option. If set to an integer, it is equivalent to specifying
|
|
:option:`-v` multiple times.
|
|
|
|
|
|
.. envvar:: PYTHONCASEOK
|
|
|
|
If this is set, Python ignores case in :keyword:`import` statements. This
|
|
only works on Windows and OS X.
|
|
|
|
|
|
.. envvar:: 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 :option:`-B` option.
|
|
|
|
|
|
.. envvar:: PYTHONHASHSEED
|
|
|
|
If this variable is not set or set to ``random``, a random value is used
|
|
to seed the hashes of str, bytes and datetime objects.
|
|
|
|
If :envvar:`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.
|
|
|
|
.. versionadded:: 3.2.3
|
|
|
|
|
|
.. envvar:: 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 :func:`str.encode`.
|
|
|
|
For stderr, the ``:errorhandler`` part is ignored; the handler will always be
|
|
``'backslashreplace'``.
|
|
|
|
.. versionchanged:: 3.4
|
|
The ``encodingname`` part is now optional.
|
|
|
|
|
|
.. envvar:: PYTHONNOUSERSITE
|
|
|
|
If this is set, Python won't add the :data:`user site-packages directory
|
|
<site.USER_SITE>` to :data:`sys.path`.
|
|
|
|
.. seealso::
|
|
|
|
:pep:`370` -- Per user site-packages directory
|
|
|
|
|
|
.. envvar:: PYTHONUSERBASE
|
|
|
|
Defines the :data:`user base directory <site.USER_BASE>`, which is used to
|
|
compute the path of the :data:`user site-packages directory <site.USER_SITE>`
|
|
and :ref:`Distutils installation paths <inst-alt-install-user>` for
|
|
``python setup.py install --user``.
|
|
|
|
.. seealso::
|
|
|
|
:pep:`370` -- Per user site-packages directory
|
|
|
|
|
|
.. envvar:: 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
|
|
Mac OS X.
|
|
|
|
.. envvar:: PYTHONWARNINGS
|
|
|
|
This is equivalent to the :option:`-W` option. If set to a comma
|
|
separated string, it is equivalent to specifying :option:`-W` multiple
|
|
times.
|
|
|
|
.. envvar:: PYTHONFAULTHANDLER
|
|
|
|
If this environment variable is set to a non-empty string,
|
|
:func:`faulthandler.enable` is called at startup: install a handler for
|
|
:const:`SIGSEGV`, :const:`SIGFPE`, :const:`SIGABRT`, :const:`SIGBUS` and
|
|
:const:`SIGILL` signals to dump the Python traceback. This is equivalent to
|
|
:option:`-X` ``faulthandler`` option.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. envvar:: PYTHONTRACEMALLOC
|
|
|
|
If this environment variable is set to a non-empty string, start tracing
|
|
Python memory allocations using the :mod:`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 :func:`tracemalloc.start` for more information.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
.. envvar:: PYTHONASYNCIODEBUG
|
|
|
|
If this environment variable is set to a non-empty string, enable the
|
|
:ref:`debug mode <asyncio-debug-mode>` of the :mod:`asyncio` module.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
Debug-mode variables
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Setting these variables only has an effect in a debug build of Python, that is,
|
|
if Python was configured with the ``--with-pydebug`` build option.
|
|
|
|
.. envvar:: PYTHONTHREADDEBUG
|
|
|
|
If set, Python will print threading debug info.
|
|
|
|
|
|
.. envvar:: PYTHONDUMPREFS
|
|
|
|
If set, Python will dump objects and reference counts still alive after
|
|
shutting down the interpreter.
|
|
|
|
|
|
.. envvar:: PYTHONMALLOCSTATS
|
|
|
|
If set, Python will print memory allocation statistics every time a new
|
|
object arena is created, and on shutdown.
|