What am I doing wrong?

[ichabod801]

As I said, lines are read in from files as strings. The readlines method gives you a list of strings. You were looping over them in appendFile before, that was fine, and was giving you individual strings. As I said, you need to convert those to integers using int().

>>> text = '1984' # a string
>>> leapYear(text) # this will give a TypeError
>>> leapYear(int(text)) # this will work