Why line 3 has no effect on list b ?

Question

a = [1,[2,3]]
b = a[:]
a[0] = 3
a[1][1] = 5
print(b)
Output is [1, [2,5]]. I was expecting it to print [3,[2,5]]

Answer 1

b is a genuine copy of a, so it has its own elements.

The list inside b however is a reference to the same list that's in a, so if you manipulate it directly, it changes in both lists (because it's actually one object).

As it happens, just yesterday I wrote a little something about how all of that works. Happy if you take a look. 🙂

https://code.sololearn.com/c89ejW97QsTN/?ref=app

Answer 2

HonFu Great tutorial. It is interesting & informative.