[issue43581] array assignment error

[John Cena]

John Cena  added the comment:

You are actually creating 4 references to the same list(See the ending *4). 
This is how python behaves. See the below link as well

https://stackoverflow.com/questions/240178/list-of-lists-changes-reflected-across-sublists-unexpectedly

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nosy: +crazyguyx4

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[issue43581] array assignment error

[Raymond Hettinger]

Change by Raymond Hettinger :


--
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue43581] array assignment error

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

By using * 4 in the end you are making four lists having same reference. Hence 
change in one causes change in other 4 lists.

Relevant FAQ : 
https://docs.python.org/3/faq/programming.html#how-do-i-create-a-multidimensional-list

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nosy: +xtreak

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[issue43581] array assignment error

[Vedran Čačić]

Vedran Čačić  added the comment:

All three words in the title are wrong. :-D

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nosy: +veky

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[issue43581] array assignment error

[Wen Hao]

New submission from Wen Hao :

>>>mat = [[0]*4]*4
>>> mat
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>> mat[1][2]=1
>>> mat
[[0, 0, 1, 0], [0, 0, 1, 0], [0, 0, 1, 0], [0, 0, 1, 0]]

--
components: Build
messages: 389230
nosy: haowenqi.zz
priority: normal
severity: normal
status: open
title: array assignment error
type: behavior
versions: Python 3.8

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