class_docstr: Base class for containers.
  
  Containers are classes that collect semantically related Artists such as
  the bars of a bar plot.
class_docstr_tok: ["Base","class","for","containers",".","Containers","are","classes","that","collect","semantically","related","Artists","such","as","the","bars","of","a","bar","plot","."]
docstr: Adds a callback function that will be called whenever one of
  the :class:`Artist`'s properties changes.
  
  Returns an *id* that is useful for removing the callback with
  :meth:`remove_callback` later.
docstr_tok: ["Adds","a","callback","function","that","will","be","called","whenever","one","of","the",":","class",":","`","Artist","`","'s","properties","changes",".","Returns","an","*","id","*","that","is","useful","for","removing","the","callback","with",":","meth",":","`","remove_callback","`","later","."]
code: def add_callback(self, func):
      """
      Adds a callback function that will be called whenever one of
      the :class:`Artist`'s properties changes.
  
      Returns an *id* that is useful for removing the callback with
      :meth:`remove_callback` later.
      """
      oid = self._oid
      self._propobservers[oid] = func
      self._oid += 1
      return oid
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import six
  import matplotlib.cbook
  import matplotlib.artist
label_desc: Use image node_id 9 for calling the Container obj's underlying member method code with example usage: obj.add_callback(func) and returns: oid