remove list element without mutation

1I assume you mean that you want to create a new list without a given element, 
2instead of changing the original list. One way is to use a list comprehension:
3
4m = ['a', 'b', 'c']
5n = [x for x in m if x != 'a']
6n is now a copy of m, but without the 'a' element.
7
8Another way would of course be to copy the list first
9
10m = ['a', 'b', 'c']
11n = m[:]
12n.remove('a')
13If removing a value by index, it is even simpler
14
15n = m[:index] + m[index+1:]