check result error.

I would like to give some feedback about ...

From: https://checkio.org/mission/flatten-list/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36

Hi. My code looks like right, but i cant pass "check result". Or its my bug? [spoiler]

b =[]
def flat_list(array):
for a in array:
    if type(a) is list: flat_list(a)
    else: b.append(a)
return b

thx for checkio.org )) Jacob