code: def fso_mkdir(self, path, mode=None):
      'overlays os.mkdir()'
      path = self.deref(path, to_parent=True)
      if self._lexists(path):
        raise OSError(17, 'File exists', path)
      self._addentry(OverlayEntry(self, path, stat.S_IFDIR)f fso_mkdir(self, path, mode=None):
      'overlays os.mkdir()'
      path = self.deref(path, to_parent=True)
      if self._lexists(path):
        raise OSError(17, 'File exists', path)
      self._addentry(OverlayEntry(self, path, stat.S_IFDIR))
docs: overlays os.mkdir()