[Tutor] How is the return statement working in this function?

[Steven D'Aprano]

Greg Christian wrote:
> I am just wondering if anyone can explain how the return statement in this
> function is working (the code is from activestate.com)? Where does x come
> from – it is not initialized anywhere else and then just appears in the
> return statement. Any help would be appreciated.

> return [2]+[x for x in s if x]

It's called a list comprehension, and is like a one-liner specialist for loop.

[x for x in s if x] builds a list using x as the loop variable. So the above 
line can be considered as the equivalent of this:

result = []
for x in s:
    if x:
        result.append(x)

return [2] + result



-- 
Steven