Best free library or database to determine if a date is a US or international holiday?

Question

In hopes of improving the relevance of year to year comparisons I would like to correct for the fact that the data last year fell on Easter, Labor Day, or whatever. What is

Answer 1

One approach is to let your users input national holidays that they know about and affect their work. You have to be careful though, at one of the IBs I worked for we noticed that one of the traders had entered National Kebab Day on his trading system as a Turkish holiday.