Days Until Next Date | Python Fiddle

"""
days_till.py:  Assignment 3, CIS 210, Fall 2012
Author:  Harold Hamm

Calculates the number of days from a given date (month, day, and year) to the 
next occurrence of another date (month and day).

"""

START_MONTH = int(input("Please enter the start month as an integer: "))
START_DAY = int(input("Please enter the day of the start month as an" 
                      " integer: "))
START_YEAR = int(input("Please enter the start year as an integer: "))

def check_start_date():
    """Determines if the start date is valid.
    
    Checks the starting month, day, and year. If the inputs fall outside the 
    accepted ranges, the program prints an error and exits.
    
    """
    days = days_in_month(START_MONTH, START_YEAR)
    
    if (START_MONTH > 12 or START_DAY > days or START_YEAR < 1800):
        print("Sorry, I need a valid date between 1/1/1800 and 12/31/2200")
        exit(1)

def days_in_month(month, year):
    """Finds the number of days in a given month.
    
    Checks the given month and year, then returns the correct number of days, 
    taking leap years into account.
    
    Args: 
        month: The given month.
        year: The given year.
    
    Returns:
        For April, June, September, or November, it returns 30. For February in 
        a leap year, it returns 29. For February not in a leap year, it returns 
        28. Otherwise, it returns 31.
    
    """
    if month == 4 or month == 6 or month == 9 or month == 11:
        days = 30
    elif month == 2:
        if leap_year(year):
            days = 29
        else:
            days = 28
    else:
        days = 31      
    return days

def leap_year(year):
    """Checks for leap years.
    
    Checks if the given year is a leap year.
    
    Args:
        year: The given year.
    
    Returns:
        True for years that are evenly divisible by 400 or 4.
        False for years that are evenly divisible by 100.
        False for any other year.
    
    """
    if year % 400 == 0 or year % 4 == 0:
       return True
    elif year % 100 == 0:
       return False
    else:
       return False

check_start_date()

END_MONTH = int(input("Please enter the end month as an integer: "))
END_DAY = int(input("Please enter the day of the end month as an"
                        " integer: "))

def check_end_date(month, day):
    """Determines if the end date is valid.
    
    Checks the ending month and day. Makes an exception for February 29. If the 
    inputs fall outside the accepted ranges, the program prints an error and 
    exits.
    
    Args:
        month: The given ending month.
        day: The day of the ending month.
        
    """
    days = days_in_month(month, end_year())
    
    if month == 2 and day == 29:
        month = 3
        day = 1
    elif month > 12 or day > days:
        print("Sorry, that month and year don't look right")
        exit(1)

def end_year():
    """Finds the ending year.
    
    Calculates if the ending year is the same as the start year or if it is the 
    next year.
    
    Returns:
        The ending year.
         
    """
    end_year = START_YEAR
    
    if END_MONTH <= START_MONTH:
        end_year = START_YEAR + 1
    return end_year

check_end_date(END_MONTH, END_DAY)

def month_days():
    """Calculates the days in each whole month.
    
    Calculates the number of days in all the whole months between the starting 
    month and the ending month.
    
    Returns:
        The number of days for all the whole months.
    
    """
    days = 0
    
    if START_MONTH == END_MONTH:
        days = 0
        
    current_month = next_month(START_MONTH)
    
    while current_month != END_MONTH:
        if end_year() == START_YEAR:
            days += days_in_month(current_month, START_YEAR)
        else:    
            days += days_in_month(current_month, end_year())            
        current_month = next_month(current_month)
    return days

def next_month(current_month):
    """Calculates the next month.
    
    Takes the current month and gives the next month.
    
    Returns:
        The next month.
    
    """
    if current_month == 12:
        next_month = 1
    else:
        next_month = current_month + 1
    return next_month

def main():
    """Calculates and prints the total days to go.
    
    Calculates and prints the total number of days between the starting date 
    and the ending date.
    
    """
    start_month_days = days_in_month(START_MONTH, START_YEAR) - START_DAY
    
    if START_MONTH == END_MONTH and END_DAY > START_DAY:
        total_days = END_DAY - START_DAY
    else:
        total_days = start_month_days + month_days() + END_DAY
    
    print(total_days, "days to go")

main()

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