A leap year is divisible by 4, not divisible by 100 only, and divisible by 400.

leap-year.py

#!/usr/bin/python

def is_leap_year (n):
    if n % 100 == 0:
        dividedBy100 = n / 100
        if dividedBy100 % 4 == 0:
            return True
    else:
        return n % 4 == 0

# From 1900 to 2000
a = [x + 1900 for x in range(101) if is_leap_year(x + 1900)]

print(len(a))
print(a)