CODEWITHSUNDEEP
pythonlistlist-comprehension
lincplus htm
lincplus htm

Reputation: 95

list comprehension change list element

I want to modify list element using list comprehension.

z=[1,2,3]
z=[z[i]=1 for i in range(len(z))]

I want to get

z=[1,1,1]

but it doesn't work.

Upvotes: 0

Views: 2213

Answers (4)

chepner
chepner

Reputation: 530922

If you want to modify z in place, use a for loop:

for i,_ in enumerate(z):
    z[i] = 1

If you want to replace the list itself (not just change the existing list), use a list comprehension:

z = [1 for _ in z]

You can't use

z = [z[i]=1 for i in range(len(z))]

because the x in [x for i in y] must be an expression, and z[i] = 1 is not an expression; it's an assignment statement.

Upvotes: 0

alani
alani

Reputation: 13049

I want to modify list element using list comprehension.

z[:] = [1 for _ in z]

or:

[z.__setitem__(i, 1) for i in range(len(z))]

These will modify the existing list rather than create a new one. You can see this if you do print(id(z)) before and afterwards. Anything starting z = will make z point to a new list.

Upvotes: 0

Itai Ben Amram
Itai Ben Amram

Reputation: 178

if you want to change all the variables of a list into the same number, using list comprehension - you're basically creating a new list... so if that's your intention it should be like this:

z = [1,2,3]
z = [1 for x in z]

Output:

[1,1,1]

Upvotes: 1

Alexander Kosik
Alexander Kosik

Reputation: 669

Use this comprehension: z = [z[0] for _ in z]

This will create a new list with the same length as the old list and will only contain the first element of the old list.

Upvotes: 0

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