in a Python program, I need to define a list from another one, and the delete an element from the new list, it also removes it from the other list. does anyone know how to counter that ?
below, an example :
source = [4, 5, 6]
new = source
new.remove(5)
print(new) # output [4, 6] has wanted
print(source) # output [4, 6] but wanted [4, 5, 6]
use copy():
source = [4, 5, 6]
new = source.copy()
new.remove(5)
print(new) #output: [4, 6]
print(source) #output: [4, 5, 6]
When you use new = source both variables point to the same place in your storage. What you need to use is:
source = [4, 5, 6]
new = source.copy()
new.remove(5)
print(new) # output [4, 6] has wanted
print(source) # output [4,5, 6] but wanted [4, 5, 6]
This will copy the elements inside the source and assign it to the new variable.
If your list contains mutable things such as objects, you should use a deep copy.
from copy import deepcopy
new = deepcopy(source)
You can use .copy() because when you use new=source the entry point will be same. So if you delete one item from one list it will delete it from both.
Code:
source = [4, 5, 6]
new = source.copy()
new.remove(5)
print(new)
print(source)
Output:
[4, 6]
[4, 5, 6]
