Python Error “list Indices Must Be Integers Not Nonetype”

I am new to python and learning the language from Udacity. I wanted to write a python program that takes 2 dates and outputs the day difference between these 2 dates, assuming the

Solution 1:

You are missing a return in your is_leap function:

def isLeap(year):
    if year%400==0:
        returnTrueelse:
        if year%100==0:
            returnFalseelse:
            if year%4==0:
                returnTrueelse:
                returnFalse  # <-- here!

Otherwise, this function will implicitly return None in that place, which is non-truthy, but not a bool, and therefore not an int (bool is a subclass of int, which makes the 0-1-index magic possible in the first place) that can be used as a list index. Btw, you do not need the else if there is a return in the if block:

def isLeap(year):
    if notyear%400:
        returnTrue
    if notyear%100:
        returnFalse
    # returnnotyear%4  # is also possible here
    if notyear%4:
        returnTruereturnFalse  # <-- needed to avoid None being returned

Whether this is more readable very often depends on the concrete circumstances. But here, with multiple nested branches, I think it helps keeping the indentation levels low and understanding what is happening.