list comprehension vs for loop, within class definition

Question

Considering the code below:

class Test:
    l = [1, 2, 3]
    foo = lambda x: x

    for x in l:
        print(foo(x))

   [print(foo(x)) for x in l]


if __name__ == '__main__':
    test = Test()

The output is the following:

1
2
3
... in <listcomp>
    [print(foo(x)) for x in l]
NameError: name 'foo' is not defined

I don't understand why isn't foo a visible function from within the list iteration. Probably something to do with scopes but I am looking for the right explanation, with documentation to support it if possible.

ps: I am not interested in alternative implementations for the sake of just fixing the code.

https://stackoverflow.com/questions/13905741/accessing-class-variables-from-a-list-comprehension-in-the-class-definition — lllrnr101, May 14 '21 at 11:27
Does this answer your question? [Accessing class variables from a list comprehension in the class definition](https://stackoverflow.com/questions/13905741/accessing-class-variables-from-a-list-comprehension-in-the-class-definition) — dejanualex, May 14 '21 at 11:30

renatodamas · Answer 1 · 2021-05-14T12:01:51.520

2

As suggested in the comments, this question seems to pretty much answer the issue and goes a long way to thoroughly explain it. There is however a small variation that can be solved following a similar approach. The resulting code is as follows:

class Test:
    l = [1, 2, 3]
    foo = lambda x: x

    (lambda foo=foo, l=l: [print(foo(x)) for x in l])()

edited May 14 '21 at 12:01

answered May 14 '21 at 11:54

renatodamas

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score 0 · Answer 2 · answered Aug 10 '21 at 01:08

0

You can also use map if your desired list comprehension is simple enough:

class Test:
    l = [1, 2, 3]
    foo = lambda x: x
    
    list(map(print, map(foo, l)))

Outputs

1
2
3

answered Aug 10 '21 at 01:08

enzo

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list comprehension vs for loop, within class definition

2 Answers2