Trying to pass by value in python 3

Asked May 05 '18 at 12:07

Active May 05 '18 at 12:10

Viewed 19 times

i'm encountering avery strange issue when programming in python 3.7:

A = [[1,2],[0,3]]
B = A[:][:]   # creates a copy of A to work with, without modify A
del B[0]

This works,well,as B becomes [[0,3]] and A is still [[1,2],[0,3]]. However, if I try this :

A = [[1,2],[0,3]]
B = A[:][:]     # creates a copy of A to work with, without modify A
del B[0][1]

B becomes [[1], [0, 3]], but A also turns into [[1], [0, 3]] ! I can't understand this behaviour,could you explain me what's happening there ?

edited May 05 '18 at 12:10

Aran-Fey

asked May 05 '18 at 12:07

EinderJam

3

`B = A[:][:]` is the same thing as `B = A[:]`. To copy multiple levels of lists, use [copy.deepcopy](https://docs.python.org/3/library/copy.html#copy.deepcopy). – Aran-Fey May 05 '18 at 12:08
Thanks,copy.deepcopy worked perfectly ! – EinderJam May 05 '18 at 12:11

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