7.18 Interview Questions

Conceptual Questions

• What is the difference between == and is?
• What is short-circuit evaluation, and why does it matter?
• Explain operator precedence with an example that would give a wrong result without it.
• What’s the difference between / and // in Python 3?
• How do bitwise operators differ in meaning between integers and sets?

Scenario-Based Questions

• A status-code check using == works for exact matches, but a range check is needed instead — how would you rewrite it using chained comparison?
• Two health-check conditions are combined with and, but the second is expensive to compute — how would you order them for best performance?
• Two config dictionaries need merging, where the second should override the first on conflicts — how do you do that in one line?

Coding Questions

• Write a function using bitwise operators to check whether a given permission flag is set in a combined permissions integer.
• Write a one-line ternary expression to classify a number as 'positive', 'negative', or 'zero'.
• Given a list of HTTP status codes, use membership/comparison operators to count how many are in the 4xx range.

Quick Interview Answer

“The core operator questions test whether the difference between identity and value (is vs ==) is understood, whether short-circuit evaluation is second nature (ordering and/or for both correctness and performance), whether precedence is trusted correctly (arithmetic before comparisons before logical), and the / vs // distinction. The coding questions almost always come down to one of: bit-flag manipulation, a ternary or chained comparison for classification, or a dict-merge one-liner.”

Common Mistakes

• Answering “is and == are basically the same” without being able to produce a concrete example where they diverge — see 7.8 Identity Operators.
• Solving the permission-flag coding question with an if/elif chain instead of perms & FLAG, missing the point of the question.
• Forgetting that {**d1, **d2} (or d1 | d2 on 3.9+) lets the second dict’s keys win on conflict — getting the override direction backwards.