def _merge_maps(m1, m2):
    """merge two Mapping objects, keeping the type of the first mapping"""
    return type(m1)(chain(m1.items(), m2.items()))
def _merge_maps ( m1 , m2 ) : return type ( m1 ) ( chain ( m1 . items ( ) , m2 . items ( ) ) )
merge two Mapping objects, keeping the type of the first mapping