def load_dynamic_class(fqn, subclass):
    """
    Dynamically load fqn class and verify it's a subclass of subclass
    """
    if not isinstance(fqn, basestring):
        return fqn

    cls = load_class_from_name(fqn)

    if cls == subclass or not issubclass(cls, subclass):
        raise TypeError("%s is not a valid %s" % (fqn, subclass.__name__))

    return cls

    Dynamically load fqn class and verify it's a subclass of subclass
    
src/diamond/utils/classes.py