How to flatten a hetrogenous list of list into a single list in python?

Question

I have a list of objects where objects can be lists or scalars. I want an flattened list with only scalars. Eg:

L = [35,53,[525,6743],64,63,[743,754,757]]
ou         


        

Answer 1

>>> data = [35,53,[525,6743],64,63,[743,754,757]]
>>> def flatten(L):
        for item in L:
            if isinstance(item,list):
                for subitem in item:
                    yield subitem
            else:
                yield item


>>> list(flatten(data))
[35, 53, 525, 6743, 64, 63, 743, 754, 757]

Here is a one-liner version for code-golf purposes (it doesn't look good :D )

>>> [y for x in data for y in (x if isinstance(x,list) else [x])]
[35, 53, 525, 6743, 64, 63, 743, 754, 757]

Answer 2

def nchain(iterable):
    for elem in iterable:
        if type(elem) is list:
            for elem2 in elem:
                yield elem2
        else:
            yield elem

Answer 3

Recursive function that will allow for infinite tree depth:

def flatten(l):
    if isinstance(l,(list,tuple)):
        if len(l):
            return flatten(l[0]) + flatten(l[1:])
        return []
    else:
        return [l]

>>>flatten([35,53,[525,[1,2],6743],64,63,[743,754,757]])
[35, 53, 525, 1, 2, 6743, 64, 63, 743, 754, 757]

I tried to avoid isinstance so as to allow for generic types, but old version would infinite loop on strings. Now it flattens strings correctly (Not by characters now, but as if it's pretending a string is a scalar).

Answer 4

outputList = []
for e in l:
    if type(e) == list:
        outputList += e
    else:
        outputList.append(e)

>>> outputList
[35, 53, 525, 6743, 64, 63, 743, 754, 757]

Answer 5

>>> L = [35,53,[525,6743],64,63,[743,754,757]]
>>> K = []
>>> [K.extend([i]) if type(i) == int else K.extend(i) for i in L ]
[None, None, None, None, None, None]
>>> K
[35, 53, 525, 6743, 64, 63, 743, 754, 757]