class_docstr: Base ``History`` interface.
class_docstr_tok: ["Base","``","History","``","interface","."]
docstr: Return the length of the history.  
docstr_tok: ["Return","the","length","of","the","history","."]
code: def __len__(self):
      "Return the length of the history."
  
imports: from __future__ import unicode_literals
  from abc import ABCMeta, abstractmethod
  from six import with_metaclass
  import datetime
  import os
label_desc: Use image node_id 4 for calling the History obj's underlying member method code with example usage: obj.__len__() without return types