Your holiday library is probably right. Here are the days it got wrong for us, and the correction layer we built

If you calculate business days, delivery dates or payroll in more than one country, you probably use the excellent open-source holidays package for Python. We do too. It covers more than 200 countries and territories and is right almost all of the time. "Almost" matters when you publish holiday lists that people plan around. So before we list a country, we compare the library's dates with the…