Question

Consider the following Python code: 

• A. Output of line Q is [10, 20]
• B. Output of line S is [10, 20, 40]
• C. Output of line R is [10, 20, 30]
• D. F1 & F2 share the same list

Hint:

Each function call to outer() creates a new closure with its own independent variable environment.

Answer 1

The Correct Option is A

The question involves understanding closures in Python and how they maintain their own environments.

Let's analyze the provided Python code step-by-step: 

1. The function outer() is defined, which initializes an empty list x.
2. Inside outer(), there's an inner function inner(val) that appends val to x and returns x.
3. outer() returns the inner function.

The code execution proceeds as follows:

1. F1 = outer() creates a new list x for F1 and assigns the inner function to F1.
2. F2 = outer() creates another new list x for F2, independent of F1's list.
3. print(F1(10)): Calls F1's function, which adds 10 to x. The list becomes [10].
4. print(F1(20)): Calls F1 again, adding 20 to x. The list becomes [10, 20].
5. print(F2(30)): Calls F2, which is independent, adding 30 to its list. The list for F2 becomes [30].
6. print(F2(40)): Calls F2 again, adding 40. The list for F2 becomes [30, 40].

Now, let's match this with the given options:

• Output of line Q is [10, 20]: This is correct since line Q refers to print(F1(20)), which indeed outputs [10, 20].
• Output of line S is [10, 20, 40]: Incorrect, as line S refers to F2(40), having no connection to the F1 list.
• Output of line R is [10, 20, 30]: Incorrect, as F1 and F2 have separate lists.
• F1 & F2 share the same list: Incorrect, they have independent lists.

Based on the above reasoning, the correct answer is:

Output of line Q is [10, 20]