Python conditional truthiness is len by default

dummy.py

class Dummy(object):
  
  def __init__(self,foo):
    self.foo = foo
  
  def __len__(self):
    #This will make me always falsy, define and __nonzero__ method!
    return 0

  def __gt__(self,other):
    return self.foo > other

  def __lt__(self,other):
    return self.foo < other

  def __eq__(self,other):
    return self.foo == other

d = Dummy(200)

if d:
  print 'This wont ever print, dummy!  Define a __nonzero__ method!'