Remove elements from a Python List

Question

I have a problem with lists in Python. I have a list of 2 different variables with the same value, but if I remove an element from any of the lists, the list that was meant to be intact also has its element removed.

listaUm = [1, 2, 3, 4]
listaDois = listaUm
listaDois.remove(3)
#listaDois [1, 2, 4]
#listaUm [1, 2, 4]

Answer 1

The reference of listaDois is equal to that of the listaUm, when you did listaDois = listaUm. So when it changes one is changing the other.

Try to copy the array this way: listaDois = [n for n in listaUm]

EDIT: As suggested by @drgarcia1986 in the comments, an equivalent form is also:

listDois = list(list one)

Answer 2

The problem with your solution is that both lists (listaUm and listaDois) reference the same place in memory.

listaUm = [1, 2, 3, 4]
listaDois = listaUm.copy() # Tire uma copia da listaUm
listaDois.remove(3)
print(listaUm)
print(listaDois)

As output, is expected [1,2,3,4] and [1,2,4].

Watch out for the remote del, because it should not be used in iterations, which can generate indexing errors

Answer 3

Use the statement del:

>>> a = [-1, 1, 66.25, 333, 333, 1234.5]
>>> del a[0]
>>> a
[1, 66.25, 333, 333, 1234.5]
>>> del a[2:4]
>>> a
[1, 66.25, 1234.5]
>>> del a[:]
>>> a
[]

Source

Answer 4

One of the valid ways to solve this problem is by performing a deep copy of list one.

This process can be obtained using the method deepcopy library copy

OBSERVING:

A deep copy builds a new composite object and then recursively inserts copies of the objects found in the original.

This way we can implement the following code:

from copy import deepcopy

listaUm = [1, 2, 3, 4]
listaDois = deepcopy(listaUm)
listaDois.remove(3)

print(listaUm)
print(listaDois)

Note that this code initially defines listDois as a deep copy of list one. Thus, listDois is a faithful copy of list one only at another memory address.

Then, from this moment we may remove any value from listDois without interfering with list one.

Executing said code, we obtain as output:

[1, 2, 3, 4]
[1, 2, 4]