join list of lists in python

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Chapters
00:00 Join List Of Lists In Python
00:20 Answer 1 Score 33
00:49 Accepted Answer Score 730
00:59 Answer 3 Score 374
01:06 Answer 4 Score 275
01:22 Thank you

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Full question
https://stackoverflow.com/questions/7164...

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Content licensed under CC BY-SA
https://meta.stackexchange.com/help/lice...

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Tags
#python

#avk47

ACCEPTED ANSWER

Score 730

import itertools
a = [['a','b'], ['c']]
print(list(itertools.chain.from_iterable(a)))

This gives

['a', 'b', 'c']

ANSWER 2

Score 374

x = [["a","b"], ["c"]]

result = sum(x, [])

ANSWER 3

Score 275

If you're only going one level deep, a nested comprehension will also work:

>>> x = [["a","b"], ["c"]]
>>> [inner
...     for outer in x
...         for inner in outer]
['a', 'b', 'c']

On one line, that becomes:

>>> [j for i in x for j in i]
['a', 'b', 'c']

ANSWER 4

Score 33

This is known as flattening, and there are a LOT of implementations out there.

How about this, although it will only work for 1 level deep nesting:

>>> x = [["a","b"], ["c"]]
>>> for el in sum(x, []):
...     print el
...
a
b
c

From those links, apparently the most complete-fast-elegant-etc implementation is the following:

def flatten(l, ltypes=(list, tuple)):
    ltype = type(l)
    l = list(l)
    i = 0
    while i < len(l):
        while isinstance(l[i], ltypes):
            if not l[i]:
                l.pop(i)
                i -= 1
                break
            else:
                l[i:i + 1] = l[i]
        i += 1
    return ltype(l)