this post was submitted on 25 Jun 2024
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Why can't I append to list inside of a list comprehension? (lemmy.world)
submitted 2 months ago* (last edited 2 months ago) by librejoe@lemmy.world to c/python@programming.dev
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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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[โ€“] polaris64@lemmy.sdf.org 2 points 2 months ago

A list comprehension is used to convert and/or filter elements of another iterable, in your case a range but this could also be another list. So you can think of it as taking one list, filtering/converting each element and producing a new list as a result.

So there's no need to append to any list as that's implicit in the comprehension.

For example, to produce a list of all squares in a range you could do:

[x*x for x in range(10)]

This would automatically "append" each square to the resulting list, there's no need to do that yourself.