def merge ( left , right , how = 'inner' , key = None , left_key = None , right_key = None , left_as = 'left' , right_as = 'right' ) : return join ( left , right , how , key , left_key , right_key , join_fn = make_union_join ( left_as , right_as ) )
inner join python means
Performs a join using the union join function .
def merge(left, right, how='inner', key=None, left_key=None, right_key=None,
          left_as='left', right_as='right'):
    """ Performs a join using the union join function. """
    return join(left, right, how, key, left_key, right_key,
                join_fn=make_union_join(left_as, right_as))