Copying mutable lists in python

Question

How not to change value of a list???

>>> a=range(0,5)
>>> b=10
>>> c=a
>>> c.append(b)
>>> c
[0, 1, 2, 3, 4, 10]
>>> a
[0, 1, 2, 3, 4, 10]

Until today i didn't know that lists in python are mutable !

Answer 1

Followng statement make c reference same list that a reference.

c = a

To make a (shallow) copy, use slice notation:

c = a[:]

or use copy.copy:

import copy

c = copy.copy(a)

---

>>> a = range(5)
>>> c = a[:]  # <-- make a copy
>>> c.append(10)
>>> a
[0, 1, 2, 3, 4]
>>> c
[0, 1, 2, 3, 4, 10]
>>> a is c
False
>>> c = a    # <--- make `c` reference the same list
>>> a is c
True