Unpack the pops

What this Python language-mechanics question tests

This is a medium-difficulty Python question that probes your understanding of core language features and how they interact in a non-obvious way. Rather than rewarding memorization, it rewards the ability to trace execution carefully and predict behaviour under specific conditions.

To solve questions like this, you need to mentally execute the code step-by-step, keeping track of state changes and understanding how Python's built-in methods and operators behave. The question is designed to catch gaps in foundational knowledge that can lead to subtle bugs in production code.

• Mutating vs. immutable data structures
• Method return values and side effects
• Order of evaluation in expressions