A Developer's Reconciliation Tool: Lessons on Decimals, Matching and Scope

The author began building a reconciliation tool after a floating-point rounding issue in Excel turned a ₦5,000.00 amount into a slightly wrong value. They chose Python's Decimal type from the start, since float arithmetic cannot represent money exactly. The first matcher found no matches because processor references like ORD-001 appeared inside longer bank descriptions, which a regex and case-insensitive comparison later resolved. The report was structured into matched, unmatched processor, and unmatched bank sections so users could focus on exceptions. The author also describes a day-by-day account of the build, including setbacks such as a command-name error that cost time.