Find day of week from month and year

[Paul Rubin]

"Laguna" <ed_zeng at yahoo.com> writes:
> I want to find the expiration date of stock options (3rd Friday of the
> month) for an any give month and year. I have tried a few tricks with
> the functions provided by the built-in module time, but the problem was
> that the 9 element tuple need to be populated correctly. Can anyone
> help me out on this one?

It's probably simplest to use the calendar module:

  http://docs.python.org/lib/module-calendar.html

see the weekday function.

> d0 = expiration(9, 2005) # d0 would be 16
> d1 = expiration(6, 2003) # d1 would be 20
> d2 = expiration(2, 2006) # d2 would be 17

# not completely tested
import calendar
def expiration(month, year):
    w1 = calendar.weekday(year, month, 1) # weekday of 1st of month
    f1d = 1 + (4-w1) % 7  # date of 1st friday
    return f1d + 14       # date of 3rd friday