how to make ["a","b",["c","d"],"e"] into ['a', 'b', 'c', 'd', 'e'] ?

[Boris Borcic]

Boris Borcic wrote:
> Rustom Mody wrote:
>>>>> def fl1(l): return [y for x in l for y in x]
>>
>>
>> # recursive flatten
>>>>> def fr(l):
>> ...   if not isinstance(l,list): return [l]
>> ...   return fl1([fr(x) for x in l])
>
> For a short non-recursive procedure - not a function, modifies L in-place but none of its sublists.
>
>  >>> def flatten(L) :
> ....    for k,_ in enumerate(L) :
> ....        while isinstance(L[k],list) :
> ....            L[k:k+1]=L[k]
>
> flattens L to any depth, eg
>
>  >>> L=[1,[2,[3,4]],5,6,[[7],8]]
>  >>> flatten(L)
>  >>> L
> [1, 2, 3, 4, 5, 6, 7, 8]

Mh, this will fail though if the last item (of the last item (of the...)) is an empty list, eg L=[[]]. If you 
want to cover this case you can wrap the inside of the proc with a try except IndexError: pass, in which case 
you can also simplify the enumerate(L) to an indefinite counter. Or insert a dummy value before starting and 
pop it off at the end.



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