Answer 1

This is different in different languages.

In Python, whatever you pass is always just a reference to the object, and the object itself decides, if you can change it or not.

So basically def f(x) means:

'When we call this function later, pass one object of whatever sort and call it by the name x.'

So if x is a number, you can't change it, if it's a list, you can. That's what 'mutable' and 'immutable' types are about.

You can then write x = whatever in your function.

But this doesn't mean that you are changing the object referred to by x - you're just stripping off the *name* x, and then you stick it to a completely different object.