Project Euler#19 Counting Sundays

#You are given the following information, but you may prefer to do some research for yourself.

#    *1 Jan 1900 was a Monday.
#    *Thirty days has September,
#    April, June and November.
#    All the rest have thirty-one,
#    Saving February alone,
#    Which has twenty-eight, rain or shine.
#    And on leap years, twenty-nine.
#    *A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.

#How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

def isLeap(year):
    """Return True for leap years, False for non-leap years."""
    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)

def add2Cal(days):
    day = 1
    weekDay = calender[-1][3]
    weekDayIndex = weekDays.index(weekDay)
    while day <= days:
        calender.append([day,month,year,weekDays[((weekDayIndex+1)%7)]])
        day += 1
        weekDayIndex = ((weekDayIndex+1)%7)



years = range(1900,2001)
months = ['Jan','Feb','March','April','May','June',\
          'July','August','Sept','Oct','Nov','Dec']
weekDays = ['Mon','Tue','Wed','Thr','Fri','Sat','Sun']
calender = [[0,0,0,'Sun']]

for year in years:
    for month in months:

        if month in ['Sept','April','June','Nov']:
            add2Cal(30)

        elif month == 'Feb' and isLeap(year):
            add2Cal(29)

        elif month == 'Feb':
            add2Cal(28)

        else:
            add2Cal(31)
count = 0

for days in calender:

    if days[2] > 1900 and days[0] == 1 and days[3] == 'Sun':
        count += 1

print count