* Add _AttributeHolder and _ActionsContainer classes to argparse.
* Add Action subclasses to argparse.
* Add _UNRECOGNIZED_ARGS_ATTR, _ensure_value, _get_action_name to argparse.
* Fill in remaining _ActionsContainer attributes.
* Fill in missing argparse.ArgumentParser attributes.
* Fill in missing argparse.HelpFormatter attributes.
* Fill in remaining missing attributes on argparse classes.
* Rename TypeVar _ActionVar to _ActionT
* Add a version check for FileType attributes
* Add '# undocumented' where appropriate
* Add more # undocumented comments
* Make arguments to _ActionsContainer.add_argument more precise.
* Have Element inherit from MutableSequence, which is more precise than Sequence.
* Remove unnecessary inherited methods (e.g., __getitem__).
* Correct extend() to take an Iterable. (Sequence was too specific.)
* Alphabetize the typing imports, for sanity.
posixpath.pyi did a '*' import of genericpath.pyi and then redefined
everything it imported. Removes the duplicate definitions from posixpath
and improves the ones in genericpath.
* Fix a few return types in stdlib/2/inspect.pyi.
* Rename _FrameRecord to _FrameInfo
* Correct some return types in itertools.pyi from Iterable to Iterator.
* Change types.pyi syntax that pytype can't parse.
* Remove types.pyi from the pytype blacklist.
* Fix a few return types in stdlib/2/inspect.pyi.
* Rename _FrameRecord to _FrameInfo
* Correct some return types in itertools.pyi from Iterable to Iterator.
* Change types.pyi syntax that pytype can't parse.
* Fix a few return types in stdlib/2/inspect.pyi.
* Rename _FrameRecord to _FrameInfo
* Correct some return types in itertools.pyi from Iterable to Iterator.