Python Coding challenge - Day 509| What is the output of the following Python Code?

 Code Explanation:

1. Function Definition

def func(a, b=[]):

Defines a function func with two parameters:

a: required argument.

b: optional argument with a default value of an empty list [].

Important: Default parameter values are evaluated once when the function is defined, so the same list b is used across calls unless explicitly overridden.

2. Append a to List b

b.append(a)

Adds the value of a to the list b.

Since b is mutable (a list), this modifies the list in place.

3. Return the List b

return b

Returns the modified list b.

4. First Call: func(1)

print(func(1))

Calls func with a=1.

Since b is not provided, it uses the default list [].

1 is appended to the list → list becomes [1].

Returns [1].

Output: [1]

5. Second Call: func(2)

print(func(2))

Calls func with a=2.

No b provided, so it uses the same default list as before (which already contains [1]).

2 is appended → list becomes [1, 2].

Returns [1, 2].

Output: [1, 2]

6. Third Call: func(3, [])

print(func(3, []))

Calls func with a=3 and explicitly passes a new empty list [] as b.

3 is appended to this new list → [3].

Returns [3].

The default list remains unchanged as this call used a fresh list.

Output: [3]

7. Fourth Call: func(4)

print(func(4))

Calls func with a=4 and no b, so it uses the default list again.

The default list currently is [1, 2] from previous calls.

4 is appended → list becomes [1, 2, 4].

Returns [1, 2, 4].

Output: [1, 2, 4]

Final Output:

[1][1, 2][3][1, 2, 4]