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179 lines
8.1 KiB
ReStructuredText
:mod:`runpy` --- Locating and executing Python modules
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======================================================
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.. module:: runpy
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:synopsis: Locate and run Python modules without importing them first.
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.. moduleauthor:: Nick Coghlan <ncoghlan@gmail.com>
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**Source code:** :source:`Lib/runpy.py`
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--------------
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The :mod:`runpy` module is used to locate and run Python modules without
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importing them first. Its main use is to implement the :option:`-m` command
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line switch that allows scripts to be located using the Python module
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namespace rather than the filesystem.
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Note that this is *not* a sandbox module - all code is executed in the
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current process, and any side effects (such as cached imports of other
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modules) will remain in place after the functions have returned.
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Furthermore, any functions and classes defined by the executed code are not
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guaranteed to work correctly after a :mod:`runpy` function has returned.
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If that limitation is not acceptable for a given use case, :mod:`importlib`
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is likely to be a more suitable choice than this module.
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The :mod:`runpy` module provides two functions:
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.. function:: run_module(mod_name, init_globals=None, run_name=None, alter_sys=False)
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.. index::
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module: __main__
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Execute the code of the specified module and return the resulting module
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globals dictionary. The module's code is first located using the standard
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import mechanism (refer to :pep:`302` for details) and then executed in a
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fresh module namespace.
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The *mod_name* argument should be an absolute module name.
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If the module name refers to a package rather than a normal
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module, then that package is imported and the ``__main__`` submodule within
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that package is then executed and the resulting module globals dictionary
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returned.
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The optional dictionary argument *init_globals* may be used to pre-populate
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the module's globals dictionary before the code is executed. The supplied
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dictionary will not be modified. If any of the special global variables
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below are defined in the supplied dictionary, those definitions are
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overridden by :func:`run_module`.
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The special global variables ``__name__``, ``__spec__``, ``__file__``,
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``__cached__``, ``__loader__`` and ``__package__`` are set in the globals
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dictionary before the module code is executed (Note that this is a
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minimal set of variables - other variables may be set implicitly as an
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interpreter implementation detail).
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``__name__`` is set to *run_name* if this optional argument is not
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:const:`None`, to ``mod_name + '.__main__'`` if the named module is a
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package and to the *mod_name* argument otherwise.
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``__spec__`` will be set appropriately for the *actually* imported
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module (that is, ``__spec__.name`` will always be *mod_name* or
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``mod_name + '.__main__``, never *run_name*).
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``__file__``, ``__cached__``, ``__loader__`` and ``__package__`` are
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:ref:`set as normal <import-mod-attrs>` based on the module spec.
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If the argument *alter_sys* is supplied and evaluates to :const:`True`,
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then ``sys.argv[0]`` is updated with the value of ``__file__`` and
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``sys.modules[__name__]`` is updated with a temporary module object for the
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module being executed. Both ``sys.argv[0]`` and ``sys.modules[__name__]``
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are restored to their original values before the function returns.
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Note that this manipulation of :mod:`sys` is not thread-safe. Other threads
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may see the partially initialised module, as well as the altered list of
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arguments. It is recommended that the :mod:`sys` module be left alone when
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invoking this function from threaded code.
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.. seealso::
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The :option:`-m` option offering equivalent functionality from the
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command line.
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.. versionchanged:: 3.1
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Added ability to execute packages by looking for a ``__main__`` submodule.
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.. versionchanged:: 3.2
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Added ``__cached__`` global variable (see :pep:`3147`).
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.. versionchanged:: 3.4
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Updated to take advantage of the module spec feature added by
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:pep:`451`. This allows ``__cached__`` to be set correctly for modules
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run this way, as well as ensuring the real module name is always
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accessible as ``__spec__.name``.
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.. function:: run_path(file_path, init_globals=None, run_name=None)
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.. index::
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module: __main__
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Execute the code at the named filesystem location and return the resulting
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module globals dictionary. As with a script name supplied to the CPython
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command line, the supplied path may refer to a Python source file, a
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compiled bytecode file or a valid sys.path entry containing a ``__main__``
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module (e.g. a zipfile containing a top-level ``__main__.py`` file).
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For a simple script, the specified code is simply executed in a fresh
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module namespace. For a valid sys.path entry (typically a zipfile or
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directory), the entry is first added to the beginning of ``sys.path``. The
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function then looks for and executes a :mod:`__main__` module using the
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updated path. Note that there is no special protection against invoking
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an existing :mod:`__main__` entry located elsewhere on ``sys.path`` if
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there is no such module at the specified location.
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The optional dictionary argument *init_globals* may be used to pre-populate
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the module's globals dictionary before the code is executed. The supplied
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dictionary will not be modified. If any of the special global variables
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below are defined in the supplied dictionary, those definitions are
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overridden by :func:`run_path`.
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The special global variables ``__name__``, ``__spec__``, ``__file__``,
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``__cached__``, ``__loader__`` and ``__package__`` are set in the globals
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dictionary before the module code is executed (Note that this is a
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minimal set of variables - other variables may be set implicitly as an
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interpreter implementation detail).
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``__name__`` is set to *run_name* if this optional argument is not
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:const:`None` and to ``'<run_path>'`` otherwise.
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If the supplied path directly references a script file (whether as source
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or as precompiled byte code), then ``__file__`` will be set to the
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supplied path, and ``__spec__``, ``__cached__``, ``__loader__`` and
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``__package__`` will all be set to :const:`None`.
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If the supplied path is a reference to a valid sys.path entry, then
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``__spec__`` will be set appropriately for the imported ``__main__``
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module (that is, ``__spec__.name`` will always be ``__main__``).
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``__file__``, ``__cached__``, ``__loader__`` and ``__package__`` will be
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:ref:`set as normal <import-mod-attrs>` based on the module spec.
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A number of alterations are also made to the :mod:`sys` module. Firstly,
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``sys.path`` may be altered as described above. ``sys.argv[0]`` is updated
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with the value of ``file_path`` and ``sys.modules[__name__]`` is updated
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with a temporary module object for the module being executed. All
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modifications to items in :mod:`sys` are reverted before the function
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returns.
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Note that, unlike :func:`run_module`, the alterations made to :mod:`sys`
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are not optional in this function as these adjustments are essential to
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allowing the execution of sys.path entries. As the thread-safety
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limitations still apply, use of this function in threaded code should be
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either serialised with the import lock or delegated to a separate process.
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.. seealso::
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:ref:`using-on-interface-options` for equivalent functionality on the
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command line (``python path/to/script``).
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.. versionadded:: 3.2
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.. versionchanged:: 3.4
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Updated to take advantage of the module spec feature added by
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:pep:`451`. This allows ``__cached__`` to be set correctly in the
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case where ``__main__`` is imported from a valid sys.path entry rather
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than being executed directly.
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.. seealso::
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:pep:`338` -- Executing modules as scripts
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PEP written and implemented by Nick Coghlan.
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:pep:`366` -- Main module explicit relative imports
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PEP written and implemented by Nick Coghlan.
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:pep:`451` -- A ModuleSpec Type for the Import System
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PEP written and implemented by Eric Snow
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:ref:`using-on-general` - CPython command line details
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The :func:`importlib.import_module` function
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