def _isClassType(t):
    """
    Compare to types.ClassType in a py2/3-compatible way

    Python 2 used comparison to types.ClassType to check for old-style
    classes Python 3 has no concept of old-style classes, so if
    ClassType doesn't exist, it can't be an old-style class - return
    False in that case.

    Note that the type() of new-style classes is NOT ClassType, and
    so this should return False for new-style classes in python 2
    as well.
    """
    _ClassType = getattr(types, 'ClassType', None)
    if _ClassType is None:
        return False
    return t == _ClassType

    Compare to types.ClassType in a py2/3-compatible way

    Python 2 used comparison to types.ClassType to check for old-style
    classes Python 3 has no concept of old-style classes, so if
    ClassType doesn't exist, it can't be an old-style class - return
    False in that case.

    Note that the type() of new-style classes is NOT ClassType, and
    so this should return False for new-style classes in python 2
    as well.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/rebuild.py