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Why can't I append to list inside of a list comprehension? (lemmy.world)

submitted 4 months ago* (last edited 4 months ago) by [email protected] to c/[email protected]

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I'm new to programming a bit, and am learning python so I can learn flask, using the python crash course book. I was learning about list comprehension but it briefly talks about it. If I do

list[list.append(value) for value in range(1, 20)]

it doesn't work. Would this be some sort of recursive expression that is not possible?

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[–] [email protected] 7 points 4 months ago* (last edited 4 months ago)

List comprehensions return a new list. For the sake of code clarity, you probably shouldn't change a second list from within a list comprehension. If you're trying to concatenate two lists, you can do so in a second line:

a = list(range(10))
b = [ value for value in range(5) ]
a.extend(b)

# a has 15 elements
print(a)