Why does python delete values in lists

Question

I have a simple code here and I am unsure as to what it is doing, please care to explain. :)

data = [5,6,7,8]

useList = data

useList.pop()
print(useList)
print(data)

For some reason the output is:

[5, 6, 7]
[5, 6, 7]

I do not understand why this occurs because I do not get rid of the 'data' value, I am only wanting to get rid of the useList value.

Is there a way to fix this?

Best Regards and any help will be openly accepted. :)

Hasan Ramezani · Accepted Answer · 2015-11-12T22:09:16.870

2

When you do useList = data you simply create another pointer to the same memory of data.

You need to create copy of data and that's done like this

useList = list(data)

Or

import copy
useList = copy.copy(data)

edited Nov 12 '15 at 22:09

answered Nov 12 '15 at 22:03

Hasan Ramezani

Oh, I see! How can I avoid this bug? I only want to delete the value of useList not data @HasanRamezani – Syed Arafat Qureshi Nov 12 '15 at 22:05
1

There is no need to import a module to create a shallow copy of a list, `old_list[:]` or `list(old_list)` is sufficient – Padraic Cunningham Nov 12 '15 at 22:08
1

Thank you @PadraicCunningham I think I will use your method instead, it looks cleaner too. – Syed Arafat Qureshi Nov 12 '15 at 22:13

1 Answers1