GATE DA 2026 Q16: Python mutable default argument output

Consider the given Python program.

def append_to_lst(val, lst=[]):
    lst.append(val)
    return lst

print(append_to_lst(1))
print(append_to_lst(2))
print(append_to_lst(3, []))

Which of the following is the correct output of this program? (Each option lists the three printed lines.)

Try it: multiple choice: exactly one correct option

Wrong answer costs 1/3 mark in GATE.

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Answer: B (official GATE 2026 final answer key)

Concept used: A default argument is created once, when the function is defined, and shared by every call that uses it.

First step: The first two calls append to the same default list; the third call passes a new empty list.

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Source: official GATE 2026 DA question paper and final answer key, organised by IIT Guwahati. Question paper · Answer key