为什么输入模块会导出“子模块”？

该typing模块导出两个类io和re作为“伪子模块”，如下所示。通过__all__将它们添加并添加到模块中，使它们看起来像模块的目的是什么sys.modules？

我理解的理由背后来自排除他们__all__：让from typing import *不会掩盖io和re如果这些都是进口的。

但是，为什么加'typing.re'和'typing.io'来sys.modules？

来自的片段typing.py：

import re as stdlib_re

# The pseudo-submodules 're' and 'io' are part of the public
# namespace, but excluded from __all__ because they might stomp on
# legitimate imports of those modules.

# ...

class io:
    """Wrapper namespace for IO generic classes."""

    __all__ = ['IO', 'TextIO', 'BinaryIO']
    IO = IO
    TextIO = TextIO
    BinaryIO = BinaryIO


io.__name__ = __name__ + '.io'
sys.modules[io.__name__] = io

Pattern = _alias(stdlib_re.Pattern, AnyStr)
Match = _alias(stdlib_re.Match, AnyStr)

class re:
    """Wrapper namespace for re type aliases."""

    __all__ = ['Pattern', 'Match']
    Pattern = Pattern
    Match = Match


re.__name__ = __name__ + '.re'
sys.modules[re.__name__] = re