input: Write a python function to determine if a given year is a leap year.
  assert is_leap_year(2000) == True
  assert is_leap_year(1900) == False
  assert is_leap_year(2012) == True
  assert is_leap_year(2019) == False
output: def is_leap_year(year):
      if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
          return True
      else:
          return False