code: def add_textbox(self, left, top, width, height):
          
          sp = self._add_textbox_sp(left, top, width, height)
          self._recalculate_extents()
          return self._shape_factory(sp)
docs: Return newly added text box shape appended to this shape tree.
  
          The text box is of the specified size, located at the specified
          position on the slide.