8.16 Interview Questions

Conceptual Questions

• What’s the difference between implicit and explicit type conversion?
• Why does int(3.9) return 3 instead of 4?
• What’s the difference between ValueError and TypeError during conversion?
• Why is bool("False") True?
• Why does input() always require explicit conversion for numeric use?

Scenario-Based Questions

• A script reads a config value "true" from a file and needs it as a real bool — how would you convert it correctly?
• An API sometimes returns a numeric field as a JSON string instead of a number — how would you defensively handle both cases?
• A CSV import is crashing on a few malformed rows — how would you make the numeric conversion resilient to bad data?

Coding Questions

• Write a safe_float() function that returns a default value instead of raising on invalid input.
• Write a function that correctly parses common boolean-like strings ("true"/"false"/"yes"/"no") into actual bool values.
• Given a list of mixed-type values, write code that converts only the ones that can be converted to int, skipping the rest.

Quick Interview Answer

“The core conversion questions test whether implicit vs explicit conversion is understood clearly, whether int()’s truncate-toward-zero behavior is known (not rounding), whether ValueError vs TypeError can be distinguished by cause, and whether the bool(\"False\") gotcha is anticipated. The coding questions almost always come down to writing a safe_* wrapper around try/except, or defensively normalizing a value that might arrive as either its real type or a string version of it.”

Common Mistakes

• Answering “int(3.9) rounds to 4” — it truncates toward zero to 3; conflating truncation with rounding is one of the most common wrong answers here.
• Writing a boolean-string parser using bool(value) directly instead of comparing lowercased text against "true" — misses the entire point of the question.
• Solving the “convert only what’s convertible” coding question with a bare except: instead of the specific (ValueError, TypeError) pair.