class_docstr: Base ``History`` interface.
class_docstr_tok: ["Base","``","History","``","interface","."]
docstr: Never evaluate to False, even when the history is empty.
  (Python calls __len__ if __bool__ is not implemented.)
  This is mainly to allow lazy evaluation::
  
      x = history or InMemoryHistory()
docstr_tok: ["Never","evaluate","to","False",",","even","when","the","history","is","empty",".","(","Python","calls","__len__","if","__bool__","is","not","implemented",".",")","This","is","mainly","to","allow","lazy","evaluation",":",":","x","=","history","or","InMemoryHistory","(",")"]
code: def __bool__(self):
      """
      Never evaluate to False, even when the history is empty.
      (Python calls __len__ if __bool__ is not implemented.)
      This is mainly to allow lazy evaluation::
  
          x = history or InMemoryHistory()
      """
      return True
  
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 5 for calling the History obj's underlying member method code with example usage: obj.__bool__() and returns: True