Learning at Udacity: My First Applied Python Code!

Woo-hoo! I've just finished my first applied Python code -- the code below returns the days between two given dates.

Congratulations to myself! :) I think this is a really tricky problem for a newbie programmer. However, with the instructions by my instructor Dave at Udacity, I finally made it! :D

The most important thing I've learned through this project is that we should break big, scaring problems down to smaller sections, then focus on solving those sections. This is pretty familiar to everyone, but I must say that I've never experienced the importance of this principle until I've done this project.

def isLeapYear(year):

    if year % 100 == 0:

        if year % 400 == 0:

            return True

    else:

        if year % 4 == 0:

            return True

    return False

        

def daysInMonth(year, month):

    if month == 1 or month == 3 or month == 5 or month == 7 or month == 8 or month == 10 or month == 12:

        return 31

    if month == 4 or month == 6 or month == 9 or month == 11:

        return 30

    if month == 2:

        if isLeapYear(year):

            return 29

        else:

            return 28

        

def nextDay(year, month, day):

    if day < daysInMonth(year, month):

        return year, month, day + 1

    else:

        if month == 12:

            return year + 1, 1, 1

        else:

            return year, month + 1, 1

        

def dateIsBefore(year1, month1, day1, year2, month2, day2):

    """Returns True if year1-month1-day1 is before year2-month2-day2. Otherwise, returns False."""

    if year1 < year2:

        return True

    if year1 == year2:

        if month1 < month2:

            return True

        if month1 == month2:

            return day1 < day2

    return False        

def daysBetweenDates(year1, month1, day1, year2, month2, day2):

    """Returns the number of days between year1/month1/day1

       and year2/month2/day2. Assumes inputs are valid dates

       in Gregorian calendar."""

    # program defensively! Add an assertion if the input is not valid!

    assert not dateIsBefore(year2, month2, day2, year1, month1, day1)

    days = 0

    while dateIsBefore(year1, month1, day1, year2, month2, day2):

        year1, month1, day1 = nextDay(year1, month1, day1)

        days += 1

    return days