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def flatten(lst):
    return sum( ([x] if not isinstance(x, list) else flatten(x)
		     for x in lst), [] )

>>> liste= [3,4,[[5]]] 
>>> test= [[[1, 2, liste], (6, [7]), 8], 9, False] 
>>> flatten(test)
[1, 2, 3, 4, 5, (6, [7]), 8, 9, False] 
>>> test
[[[1, 2, [3, 4, [[5]]]], (6, [7]), 8], 9, False] 
>>> liste
[3, 4, [[5]]] 

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>>> liste= [3,4,[[5]]] 
>>> test= [[[1, 2, egg], (6, [7]), 8], 9, False] 
>>> flatten_in_place(test) 
>>> test
[1, 2, 3, 4, 5, (6, [7]), 8, 9, False]
>>> liste
[3, 4, 5]