# isLeapYear-7.11.py
# Determine whether a year greater than 0 is a leap year
# Neal Nelson  2007.11.07

# This program illustrates program organization using functions, 
# exceptions, and conditional execution of main (so the module can
# also be used as an import).

def isLeapYear(year):
  # A leap year is any year divisible by 4 except centuries not
  # divisible by 400
  return (year % 4 == 0) and not ((year % 100 == 0 and year % 400 != 0))

def main():
  print "This program determines whether a calendar year is a leap year"

  try:
    year = input("Enter a year greater than 0 (eg: 1976): ")
    if year <= 0: 
      # force an exception until we know how to properly define
      # our own exceptions and raise them. This is a kludge for now,
      # but better than cluttering up our program.
      1/0  

    if isLeapYear(year):
      print "Yes, %d is a leap year" % year
    else:
      print "No, %d is not a leap year" % year

  except:
    print "An input year must be an integer greater than 0."


# Execute main only if this file is invoked directly from Python
if __name__ == "__main__":
  main()