Python 3.2 UnboundLocalError in Date to Day of the Week converter

Question

Nooby Coder here! My assignment is to code something that prints the day of the week of any given date. My code is working fine but when I run anything that isn't in the correct format (i.e. "//2011" or "12/a/2011") it will give me this error:

line 55, in main if is_date_valid(month, day, year) == False:
UnboundLocalError: local variable 'month' referenced before assignment

Although it does run fine if I try "13/2/2011". Please help me find my problem, as my teacher didn't know the solution when I asked him about it! Here is the whole code if necessary (ignore my comments :p) Thank you very much :D

import sys
DAYS_IN_MONTH = ('31', '28', '31', '30', '31', '30', '31', '31', '30', '31', '30', '31')
MONTHS_IN_WORDS = ("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December")
DAYS_OF_WEEK = ('Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday')

def get_date():
    str_date = input('Enter date: ')#.strip() = method :D
    parts = str_date.split('/')#pasts = ['12', '2', '2011']
    length = len(parts)
    if length != 3:
        raise ValueError('Invalid format for date.')
    for i in range(length):
        parts[i] = parts[i].strip()
        if len(parts[i]) == 0 or not(parts[i].isdigit()):
            raise ValueError('Invalid format for date.')
    return(int(parts[0]), int(parts[1]), int(parts[2]))

def is_date_valid(month, day, year): #is_date_valid = name of function
    if month < 1 or month > 12 or day < 1 or year < 0:
        return False
    if month != 2:
        return int(day) <= int(DAYS_IN_MONTH[month-1])
    additional = 0
    if year % 400 == 0 or year % 4 == 0 and year % 100 != 0:
        additional = 1
    return int(day) <= int(DAYS_IN_MONTH[1]) + int(additional)

#month, day, year = arguments of function

def date_as_string(month, day, year):
    if month > 0 and month < 13:
        return MONTHS_IN_WORDS[month-1] + ' ' + str(day) + ', ' + str(year)


def day_of_week(month, day, year):
    if month < 3:
        month += 12
        year -= 1
    m = month
    q = day
    J = year // 100
    K = year % 100
    h = (q + 26*(m+1)//10 + K + K//4 + J//4 - 2*J) % 7
    dayweek = DAYS_OF_WEEK[h-2]
    return dayweek

def main():
    print('This program calculates the day of the week for any date.')
    try:
        (month, day, year) = get_date()
    except ValueError as error:
        print("ERROR:", error)
        sys.exit(1)
    if is_date_valid(month, day, year) == False:
        print(str(month) + '/' + str(day) + '/' + str(year) + ' is an invalid date.')
        print()

    else: 
        print(date_as_string(month, day, year) + ' is a ' + day_of_week(month, day, year) + '.')
        print()



#any function call that can raise an error must be put inside a try block
if __name__ == '__main__':
    main()

score 0 · Answer 1 · answered Dec 11 '11 at 09:21

Firstly, you enter a date with no month, your program will tell you that you don't have a month. This doesn't seem to be much of a problem?

Secondly, and both your examples will in fact give a "ERROR: Invalid format for date.", and not the exception you claim. Your last example. 13/2/2011, will give "13/2/2011 is an invalid date.", but if you change it to a valid date, like "12/2/2011" it will give "February 13, 2011 is a Sunday."

Hence your program is working perfectly.

Python 3.2 UnboundLocalError in Date to Day of the Week converter

1 Answers1