Cam, I did not noticed that this is not built-in python. It seems I had it installed already.
The reason I used it to make a 2 years of datatime values, so I made first month and then added 24 months to it.
Alternate options are:
1- use 1 year for datetime values in test code and use list instead.
2- use a code that does not require dependency for increasing month for more than year

working on it.....