text: Problem with abstract classes
  Bug Description
  The following test:
  def test_remove_
  class AbstractSeriali
  pass
  class ConcreteSeriali
  pass
  class MyConcreteSeria
  pass
  Ends up with the following error in python 2.7:
  Traceback (most recent call last):
  File "debtcollector/
  class MyConcreteSeria
  File "/Users/
  cls = super(ABCMeta, mcls).__new__(mcls, name, bases, namespace)
  TypeError: Error when calling the metaclass bases
  metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases
  And ends up with the following error in python 3.4:
  Traceback (most recent call last):
  File "/Users/
  MyConcreteS
  TypeError: 'tuple' object is not callable
  Note that this showed up in a real life situation :) when we added deprecation to RequestContextS
  erializer in oslo.messaging and we will be breaking ironic:
  https:/
  /s3.amazonaws. com/archive. travis- ci.org/ jobs/93447606/ log.txt /s3.amazonaws. com/archive. travis- ci.org/ jobs/93447607/ log.txt
  https:/