':raises ValueError: If specified visibility timeout exceeds MAXIMUM_VISIBILTY_TIMEOUT
:raises TypeError: If visibility timeout was not specified'

def _get_validated_visibility_timeout(self):

    visibility_timeout = int(self.querystring.get(u'VisibilityTimeout')[0])
    if (visibility_timeout > MAXIMUM_VISIBILTY_TIMEOUT):
        raise ValueError
    return visibility_timeout
