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 4 months ago* (last edited 4 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€“] onlinepersona@programming.dev 0 points 4 months ago

Sure you can. As others have said, a list comprehension returns a new list. See the documentation.

What are you trying to do though? Append a list comprehension to an existing list?

See a modified version of @eager_eagle@lemmy.world's code from their comment.

def double(x):
  return 2 * x
a = list(range(10))
a.extend(double(value) for value in range(5))

# a has 15 elements
print(a)

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