Search for an attribute (attr) in class list (cls_list). Returns
    attribute value if exists or None if not.

def getattr_in_cls_list(cls_list, attr, default):
    """ Search for an attribute (attr) in class list (cls_list). Returns
    attribute value if exists or None if not. """
    for cls in cls_list:
        if hasattr(cls, attr):
            return getattr(cls, attr)
    return default