Flatten a List on O'Reilly

I would like to give some feedback about https://py.checkio.org/mission/flatten-list/legacy-solve/ ... it appears the system only starts new and fresh locally inside the defined function. The variable I've assigned outside the function maintains its value from the last assertion test.

I tried to rectify this issue by making the variable global, but to no avail. The solution works in an IDE, obviously, in my case, I'm using PyCharm. Is this not a valid or acceptable way to complete this particular challenge? The code I used is as follows:

nums = []


def flat_list(array):
    for item in array:
        if type(item) is list:
            flatten(item)
        elif type(item) is int:
            nums.append(item)
    return nums

I've included some screenshots showing the different output from my end. The function name and variable names have been changed to protect the innocent :P

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