Most Python files should include the following boilerplate at the top of the file, right after the comment header and from __future__ import:

__metaclass__ = type

Python 2 has “new-style classes” and “old-style classes” whereas Python 3 only has new-style classes. Adding the __metaclass__ = type boilerplate makes every class defined in that file into a new-style class as well.

from __future__ import absolute_import, division, print_function
__metaclass__ = type

class Foo:
    # This is a new-style class even on Python 2 because of the __metaclass__