The Counter That Counted a Call the Preflight Never Reached

This is a submission for DEV's Summer Bug Smash: Clear the Lineup , powered by Sentry . Project Overview I was working on a small Python component that performs a preflight check and then, if the check succeeds, invokes one synchronous operation callback. A counter records whether that callback invocation returned normally. The counter is used for diagnostics, so it must follow the control flow rather than the expected happy path. Bug Fix or Performance Improvement When a handled failure occurred, the old implementation still returned one: return 1 That value was hard-coded because the successful path was expected to invoke exactly one operation. If the preflight check failed, however, the operation was never entered and the function still returned one. An offline reproduction produced: operation_entries=0 old_count=1 The failure was handled, but the counter contradicted the actual control flow. Code Reduced to the relevant lines, the old behavior was: # Simplified pre-fix behavior def buggy_completed_calls ( * , preflight , operation ): try : preflight () operation () except Exception : pass return 1 Here is the complete fixed function from the standalone reproducer: from collections.abc import Callable Callback = Callable [[], None ] def completed_calls ( * , preflight : Callback , operation : Callback ) -> int : """ Return one only when the cooperative operation returned normally. """ try : preflight () operation () except Exception : return 0 return 1 The essential regression assertion is shown below. Both callbacks are local, so the test performs no network request: # Abbreviated test excerpt def test_preflight_failure_does_not_count_an_unentered_operation (): operation_entries = 0 def refuse_preflight (): raise RuntimeError ( " controlled preflight refusal " ) def operation (): nonlocal operation_entries operation_entries += 1 result = completed_calls ( preflight = refuse_preflight , operation = operation , ) assert operation_entries == 0 assert result == 0 My