Stripe·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Stripe debugging interview for a software engineer role. They handed me a small Python program using the Mako template engine with three planted bugs and told me to find them using a debugger. Two needed actual code fixes, the third just a verbal explanation. Felt more like a practical lab than a traditional coding round.

Questions Asked (1)

You are given a small Python program built on the Mako template engine containing three bugs. Use a debugger to reproduce each bug, trace the root cause, fix the first two in code, and verbally describe the fix for the third.

Root Cause AnalysisTechnical Trade-offs

Author's notes

This was not what I expected from a Stripe screen.

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AI HintsAI Generated

Suggested Approach

Start by reproducing each bug with the debugger to understand the failure, then trace the root cause by inspecting variables and call stack. Fix the first two bugs in code with minimal changes, and for the third, clearly explain the fix and why it works. Throughout, verbalize your reasoning and trade-offs.

Pro tip: Before diving into the debugger, quickly scan the code for common Mako pitfalls like missing imports, incorrect context variables, or unescaped expressions. This often narrows down where to set breakpoints and shows structured thinking.

1. Reproduce and Observe

Run the program under the debugger, trigger each bug, and note the exact error messages and stack traces. Set breakpoints at key points to observe the program state.

2. Trace Root Cause

Step through the code, inspect variables, and follow the call stack to identify why the bug occurs. Distinguish between symptoms and underlying causes.

3. Fix First Two Bugs

Implement minimal code fixes for the first two bugs, ensuring they address the root cause without introducing regressions. Re-run to verify.

4. Describe Third Fix

Verbally explain the root cause of the third bug and the exact code change you would make, including any trade-offs or alternative solutions.

5. Summarize and Reflect

Summarize the fixes, discuss any lessons learned, and mention how you would prevent similar bugs in the future (e.g., tests, code review).

Key Points to Mention

Use of debugger features: breakpoints, step over/into, watch expressions, call stack inspection.
Mako-specific issues: context variables, template inheritance, expression escaping, and compile-time errors.
Root cause analysis: distinguishing between symptoms and underlying causes, and verifying with tests.
Trade-offs in fixes: minimal change vs. refactoring, performance impact, and maintainability.
Communication: verbalizing thought process clearly, especially for the third bug.
Preventive measures: adding unit tests, logging, and static analysis to catch similar bugs.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.