Why can a function modify some arguments as perceived by the caller, but not others?

Question

I\'m trying to understand Python\'s approach to variable scope. In this example, why is f() able to alter the value of x, as perceived within

Answer 1

f doesn't actually alter the value of x (which is always the same reference to an instance of a list). Rather, it alters the contents of this list.

In both cases, a copy of a reference is passed to the function. Inside the function,

• n gets assigned a new value. Only the reference inside the function is modified, not the one outside it.
• x does not get assigned a new value: neither the reference inside nor outside the function are modified. Instead, x’s value is modified.

Since both the x inside the function and outside it refer to the same value, both see the modification. By contrast, the n inside the function and outside it refer to different values after n was reassigned inside the function.