flatten a python list of lists

flatten_list.py

# source: flatten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else [x]

def flatten(x):
    if type(x) == list:
        a = []
        for l in x:
            for y in flatten(l):
                a.append(y)
        return a
    else:
        return [x]
        

# ----------------- demo ----------------------

>>> a = [1, 2, [3, 4], [[5, 6], [7, 8]]]
>>> flatten(a)
[1, 2, 3, 4, 5, 6, 7, 8]