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Issue #19697: document more __main__.__spec__ quirks

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Nick Coghlan 2014-03-29 15:39:42 +10:00
parent e08f376ed2
commit 9aa00d1cd1
1 changed files with 16 additions and 2 deletions
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18
Doc/reference/import.rst
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@ -852,16 +852,30 @@ Depending on how :mod:`__main__` is initialized, ``__main__.__spec__``
gets set appropriately or to ``None``.
When Python is started with the :option:`-m` option, ``__spec__`` is set
to the module spec of the corresponding module.
to the module spec of the corresponding module or package. ``__spec__`` is
also populated when the ``__main__`` module is loaded as part of executing a
directory, zipfile or other :data:`sys.path` entry.
In :ref:`the remaining cases <using-on-interface-options>`
``__main__.__spec__`` is set to ``None``:
``__main__.__spec__`` is set to ``None``, as the code used to populate the
:mod:`__main__` does not correspond directly with an importable module:
- interactive prompt
- -c switch
- running from stdin
- running directly from a source or bytecode file
Note that ``__main__.__spec__`` is always ``None`` in the last case,
*even if* the file could technically be imported directly as a module
instead. Use the :option:`-m` switch if valid module metadata is desired
in :mod:`__main__`.
Note also that even when ``__main__`` corresponds with an importable module
and ``__main__.__spec__`` is set accordingly, they're still considered
*distinct* modules. This is due to the fact that blocks guarded by
``if __name__ == "__main__":`` checks only execute when the module is used
to populate the ``__main__`` namespace, and not during normal import.
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