list comprehension question

Arnaud Delobelle arnodel at
Fri May 1 02:28:51 EDT 2009

Ross <ross.jett at> writes:

> If I have a list of tuples a = [(1,2), (3,4), (5,6)], and I want to
> return a new list of each individual element in these tuples, I can do
> it with a nested for loop but when I try to do it using the list
> comprehension b = [j for j in i for i in a], my output is b =
> [5,5,5,6,6,6] instead of the correct b = [1,2,3,4,5,6]. What am I
> doing wrong?

When writing nested list comprehension, the for loops are in the same
order as you would write a normal nested for loop (which is not
necessarily intuitive when you first find out but is very handy in the
long run I think).

So write:

    [j for i in a for j in i]


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