When is “i += x” different from “i = i + x” in Python?

Question

I was told that += can have different effects than the standard notation of i = i +. Is there a case in which i += 1 would be differen

Answer 1

Here is an example that directly compares i += x with i = i + x:

def foo(x):
  x = x + [42]

def bar(x):
  x += [42]

c = [27]
foo(c); # c is not changed
bar(c); # c is changed to [27, 42]