What does a list comprehension do

[Marko Rauhamaa]

Antoon Pardon <antoon.pardon at rece.vub.ac.be>:

> Personnaly I would prefer:
>
>>>> q = [(lambda i: lambda x: i * x)(i) for i in range(4)]
>>>> q[0](1), q[3](1)
> (0, 3)
>
> And this is where I ask whether it would be worth the effort to change
> the behaviour of python.

Don't go there.

Consider:

    q = []
    n = 0
    x = "hello"

    for i in range(4):
        def stepper():
            global n
            n += 1
            return i * x
        q.append(stepper)

    print(n)
    print(q[1]())
    print(n)
    x = "there"
    print(q[3]())
    print(n)

which prints:

    0
    hellohellohello
    1
    theretherethere
    2

after your change, you'd get:

    0
    hello
    0
    hellohellohello
    0

> It also seems that people who try this for the first time are
> surprised with what they get and seem to expect there list
> comprehension to act as if they had written the second version.

I might trip over that one, too. Still, nothing should be changed.


Marko