Calculate every interval of days between 2 dates.

interval.py

import datetime
import sys

year = int(sys.argv[1])

def calculate(year):
    dt1 = datetime.datetime(year, 1, 1)
    yield ("A", dt1)

    dt2 = datetime.timedelta(days=14)

    for i in range(25):            
        yield (chr(66+i),dt1+dt2)
        dt1=dt1+dt2

for letter, date in calculate(year):
    real_date = date.strftime("%Y %b %d")
    print (letter, real_date)