birthday.py

from datetime import datetime

number_endings = {
    1: 'st',
    2: 'nd',
    3: 'rd'
}

today = datetime.now()
todays_day = today.day

# get the right ending, e.g. 1 => 1st, 2 => 2nd
# but beware! 11 => 11th, 21 => 21st, 31 => 31st

# test your code by forcing todays_day to be something different
# todays_day = 11

def find_ending(day):
	ending = 'th'
	if day < 10 or day > 20:
    	# x % y (mod) will give the remainder when x is divided by y
    	# -- but x needs to be an integer!
		number = day % 10
    	# look up number in number_endings
    	# and if you find it as a key, put the value in ending
    	if number in number_endings:
    		ending = number_endings[number]
	return ending


# make this print ending, not 'th'
print "Today is the " + str(todays_day) + find_ending(todays_day) + "."

birthday = int(raw_input("What day of the month is your birthday? "))

# make this print the birthday, and the right ending
print "Your birthday is on the " + str(birthday) + find_ending(birthday) + "!"