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 1:mod:`runpy` --- Locating and executing Python modules
 2======================================================
 3
 4.. module:: runpy
 5   :synopsis: Locate and run Python modules without importing them first.
 6.. moduleauthor:: Nick Coghlan <ncoghlan@gmail.com>
 7
 8
 9.. versionadded:: 2.5
10
11The :mod:`runpy` module is used to locate and run Python modules without
12importing them first. Its main use is to implement the :option:`-m` command line
13switch that allows scripts to be located using the Python module namespace
14rather than the filesystem.
15
16When executed as a script, the module effectively operates as follows::
17
18   del sys.argv[0]  # Remove the runpy module from the arguments
19   run_module(sys.argv[0], run_name="__main__", alter_sys=True)
20
21The :mod:`runpy` module provides a single function:
22
23
24.. function:: run_module(mod_name[, init_globals] [, run_name][, alter_sys])
25
26   Execute the code of the specified module and return the resulting module globals
27   dictionary. The module's code is first located using the standard import
28   mechanism (refer to PEP 302 for details) and then executed in a fresh module
29   namespace.
30
31   The optional dictionary argument *init_globals* may be used to pre-populate the
32   globals dictionary before the code is executed. The supplied dictionary will not
33   be modified. If any of the special global variables below are defined in the
34   supplied dictionary, those definitions are overridden by the ``run_module``
35   function.
36
37   The special global variables ``__name__``, ``__file__``, ``__loader__`` and
38   ``__builtins__`` are set in the globals dictionary before the module code is
39   executed.
40
41   ``__name__`` is set to *run_name* if this optional argument is supplied, and the
42   *mod_name* argument otherwise.
43
44   ``__loader__`` is set to the PEP 302 module loader used to retrieve the code for
45   the module (This loader may be a wrapper around the standard import mechanism).
46
47   ``__file__`` is set to the name provided by the module loader. If the loader
48   does not make filename information available, this variable is set to ``None``.
49
50   ``__builtins__`` is automatically initialised with a reference to the top level
51   namespace of the :mod:`__builtin__` module.
52
53   If the argument *alter_sys* is supplied and evaluates to ``True``, then
54   ``sys.argv[0]`` is updated with the value of ``__file__`` and
55   ``sys.modules[__name__]`` is updated with a temporary module object for the
56   module being executed. Both ``sys.argv[0]`` and ``sys.modules[__name__]``
57   are restored to their original values before the function returns.
58
59   Note that this manipulation of :mod:`sys` is not thread-safe. Other threads may
60   see the partially initialised module, as well as the altered list of arguments.
61   It is recommended that the :mod:`sys` module be left alone when invoking this
62   function from threaded code.
63
64
65.. seealso::
66
67   :pep:`338` - Executing modules as scripts
68      PEP written and  implemented by Nick Coghlan.
69