python list comprehension for loop in for loop

Question

What the beat way to convert:

[(1, 2), (3, 4)] => [1, 2, 3, 4]

I tried

[i for i in row for row in [(1, 2), (3, 4)]]

but it's not work.

Yes, it's a dumplicate question in some kind. I just can't find it(I don't know how to expression this question). Thanks for your mention. — Xiaorong Liao, Dec 04 '15 at 06:25

score 2 · Answer 1 · answered Dec 04 '15 at 06:16

2

You can do this also with chain from itertools

from itertools import chain
a = [(1, 2), (3, 4)]
print(list(chain.from_iterable(a)))

>>>>[1, 2, 3, 4]

answered Dec 04 '15 at 06:16

JDurstberger

John La Rooy · Answer 2 · 2015-12-04T06:29:05.670

1

A list comprehension is the best way to do this

>>> L = [(1, 2), (3, 4)]
>>> [j for i in L for j in i]
[1, 2, 3, 4]

Note that the "outer loop" variable needs to come first

edited Dec 04 '15 at 06:29

answered Dec 04 '15 at 06:15

John La Rooy

score 1 · Answer 3 · answered Dec 04 '15 at 06:15

1

>>> [i for row in [(1, 2), (3, 4)] for i in row]
[1, 2, 3, 4]
>>>

[i for row in [(1, 2), (3, 4)] for i in row]
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^  # you need define 'row' before define 'i'

answered Dec 04 '15 at 06:15

Remi Guan

3 Answers3