Mutable/immutable data types and object copies

[tavareshugo]

This document might be a nice inspiration for the distinction of mutable/immutable types, and how it relates to memory and making copies of objects.

To me (coming from R) it's easy to forget that the following code would result in a being changed:

a = [1, 2, 3]
b = a
b.append(4)   # both a and b become [1, 2, 3, 4]

It might be worth flagging this up with an example/exercise, as it might cause people silent bugs if they come from another language.