Question 1

Implicit None return

Accepted Answer

A function that never executes a return statement returns None. The expression x * 2 is evaluated but its result is immediately discarded because there is no return keyword. The most tempting wrong answer is 10, but that would require writing return x * 2. Forgetting return is one of the most common silent bugs in Python - the function runs without error and just hands back nothing.

Question 2

Default argument evaluation

Accepted Answer

Default values are evaluated exactly once at function definition time, not on each call. That's why using a mutable object like a list as a default is a classic bug - all calls share the same list object. The fix is to use None as the default and create the mutable object inside the function body. Many developers assume defaults are re-evaluated per call, which is why this catches people off guard.

Question 3

Reading from enclosing scope

Accepted Answer

Python's LEGB rule means a function can read a variable from an outer (global) scope without any special declaration. show() has no local x, so Python moves up to the global scope and finds x = 10. You only need global or nonlocal when you want to assign to a name in an outer scope - reading is free.