def __getitem__(self, key):
        """Retrieve a file from one of the contained groups.

        The key is verified in order to make certain assumptions later on.
        If it is valid, the correct file is returned after parsing the key."""
        if key not in self:
            raise KeyError(repr(key) + ' NOT FOUND IN LIBRARY')
        if '.' in key:
            group, file = list(map(int, key.split('.')))
        else:
            group, file = None, int(key)
        if group is None:
            group = self.__option
        else:
            group = self.__groups[group]
        return group[file]
Retrieve a file from one of the contained groups.

        The key is verified in order to make certain assumptions later on.
        If it is valid, the correct file is returned after parsing the key.
recipes/Python/577049_Bible_Verse_Quiz__librarypy/recipe-577049.py