I have an Excel workbook containing roughly 20,000 rows. Column A lists “Pincode 1”, Column B lists “Pincode 2”. I need Column C populated with the road-driving distance (in kilometres) for every pair. What I need from you • A Python-based solution — a clean, well-commented script or small CLI tool. • It should open the existing .xlsx, loop through all rows, query a mapping service for the driving distance, write the result back into a third column, and save a new file. • Feel free to use Google Maps Distance Matrix, Mapbox Directions, OpenRouteService, or any similar API; just keep the call structure modular so I can drop in a different key or provider if needed. • Please include simple rate-limit handling (sleep / exponential back-off is fine) and an optional, lightweight cache so repeated pincode pairs don’t re-trigger an API call. • Final hand-off: source code, requirements.txt, and a short README explaining setup, environment variables (for the API key), and how to run the script on Windows. Acceptance checklist 1. Script completes without unhandled errors on my sample of 20k rows. 2. Output file retains original two columns and adds an accurate “Distance_km” column. 3. Results verified spot-check against the live API return the same values (± the API’s rounding). If you have done similar large-batch geocoding or distance-matrix work, let me know — that experience will help me trust your approach. Otherwise, a concise outline of the API you plan to use and how you’ll avoid quota issues is enough for me to decide quickly.