Python why would you use [:] over =

Question

I am just learning python and I am going though the tutorials on https://developers.google.com/edu/python/strings

Under the String Slices section

Answer 1

They have the same value, but there is a fundamental difference when dealing with mutable objects.

Say foo = [1, 2, 3]. You assign bar = foo, and baz = foo[:]. Now let's say you want to change bar - bar.append(4). You check the value of foo, and...

print foo
# [1, 2, 3, 4]

Now where did that extra 4 come from? It's because you assigned bar to the identity of foo, so when you change one you change the other. You change baz - baz.append(5), but nothing has happened to the other two - that's because you assigned a copy of foo to baz.

Note however that because strings are immutable, it doesn't matter.