def _double_prefix(deque):
 new_len = max((len(deque[0]) * 2), (len(deque[0]) + len(deque[1])))
 _merge_prefix(deque, new_len)

def _double_prefix ( deque ) : new_len = max ( ( len ( deque [ 0 ] ) * 2 ) , ( len ( deque [ 0 ] ) + len ( deque [ 1 ] ) ) ) _merge_prefix ( deque , new_len )
grow by doubling .