The big difference is that the first function may be be wrong, but the second is quite obviously wrong. The smallest odd of a list of numbers > 9999 is not 999

The big difference is that the first function may be be wrong, but the second is quite obviously wrong. The smallest odd of a list of numbers > 9999 is not 9999. The smallest odd of an empty list is 9999 is not 9999. The smallest odd of a list of even numbers is not 9999. The first function does seem easier to understand but relies on global state (is_end_of_week, is_end_of_month) and side effecting functions (run_payroll). Neither of these functions should survive code review.