How a misplaced Python import silently broke a caching feature for months

A developer reviewing an open-source instrument-control library discovered a caching feature that had never worked, not due to a crash but due to complete silence. The root cause was a conditional 'import json' statement inside a function branch, which Python's compile-time scoping rules treated as a local variable throughout the entire function, causing an UnboundLocalError when accessed on a mutually exclusive branch. Instead of surfacing this error, a broad 'except Exception: pass' handler swallowed it every time, leaving no log, no traceback, and no visible failure. As a result, manual connections were never cached, auto-discovery never learned from them, and the library performed a full device scan on every call — the exact overhead the cache was designed to eliminate. The incident highlights two compounding pitfalls: placing imports inside conditionals and using overly broad exception handlers that silently discard errors.