+- Python Forum (https://python-forum.io)
+-- Forum: Python Coding (https://python-forum.io/forum-7.html)
+--- Forum: General Coding Help (https://python-forum.io/forum-8.html)
+--- Thread: Why changing data in a copied list changes the original list? (/thread-34594.html)
Why changing data in a copied list changes the original list? - plumberpy - Aug-12-2021
results=[[1,2,3,4,5],
[11,22,33,44,55],
[111,222,333,444,555]]
#results2=results.copy()
results2=results[:]
results2[2][0]='A'
results2[2][1]='B'
results2[2][2]='C'
print(results, results2)Using .copy() and [:], data in the original list is also changed when I changed the data in the copied list.How can I have 2 independent copied lists?
Thanks.
P/S Found the answer.
import copy #lst_copy = copy.deepcopy(lst) #results2=results.copy() results2=copy.deepcopy(results) results2[2][0]='A' results2[2][1]='B' results2[2][2]='C' print(results, results2)What is the benefit in making a copy and changing the copied will change the original? Wish that it is just like normal copy.
RE: Why changing data in a copied list changes the original list? - Larz60+ - Aug-12-2021
use deepcopy to create physical copy (instead of reference): https://docs.python.org/3/library/copy.html
which I see you are already using.
RE: Why changing data in a copied list changes the original list? - jefsummers - Aug-12-2021
A great video that explains the whys and hows of this is Ned Batchelder's talk from PyCon 2015 at https://www.youtube.com/watch?v=_AEJHKGk9ns
RE: Why changing data in a copied list changes the original list? - plumberpy - Aug-14-2021
(Aug-12-2021, 01:49 PM)jefsummers Wrote: A great video that explains the whys and hows of this is Ned Batchelder's talk from PyCon 2015 at https://www.youtube.com/watch?v=_AEJHKGk9ns
Many thanks.