[dwattttt]

So to be very clear:

  def foo(x):
    x['a'] = 1
  
  y = {'b': 2}
  foo(y)
  print(y)

foo can modify the object y points to, but it can't make y point to a different object? Is that what "This is impossible in Python" is referring to?

[tsimionescu]

Yes.