GIL

What this Python GIL question tests

This is an easy conceptual question about Python's Global Interpreter Lock (GIL), commonly asked in quant interviews to assess whether a candidate understands a fundamental constraint of the CPython runtime. It is not a puzzle; it tests baseline language knowledge.

The question asks you to explain what the GIL is, why it exists, and what practical implications it has for concurrent programming in Python. Quant firms ask this because it directly affects how you design multi-threaded systems for market data ingestion, order routing, and real-time analytics. A strong answer demonstrates that you understand the difference between true parallelism and concurrency, and that you know when the GIL is a bottleneck and when it is not.

• Threading vs. multiprocessing trade-offs
• CPU-bound vs. I/O-bound workloads
• Reference counting and memory safety in CPython