pyLeapYearTest

#  Function to test if a year is a Leap Year
#  Mike Kerry - Feb-2021 - [email protected]


def leap_year(year):
    if year & 3:
        return False
    if not year % 400:
        return True
    return year % 100


# Here is a copy of the above function with comments:-
def leap_year_copy(year):
    # This bit-wise test is faster than year % 4. It examines the 2 low-order bits of the year.
    # If either a 1-bit or a 2-bit are present, then the year is not a multiple of 4. Hence not Leap.
    if year & 3:
        return False

    # If the year is divisble by 400 (i.e. there is no remainder - hence the "not"), then the year is Leap
    if not year % 400:
        return True

    # Now we know that the year is a multiple of 4, but is not a multiple of 400

    # Examine the remainder of dividing year by 100. If the remainder is zero, it is not Leap
    # If the remainder is not zero, then it is a Leap year
    # Hence in either case we can simply return the remainder,
    # which will be treated as True if there is a remainder, (e.g. year 1904)
    # and False if no remainder (e.g. year 1900)
    return year % 100


tests = [1899, 1900, 1901, 1902, 1904, 1999, 2000, 2001, 2002,
         2003, 2004, 2015, 2016, 2017, 2018, 2019, 2020, 2021]

for t in tests:
    word = ""
    if not leap_year(t):
        word = "not"
    print("The year", t, "is", word, "a leap year")


# Output:
#
# The year 1899 is not a leap year
# The year 1900 is not a leap year
# The year 1901 is not a leap year
# The year 1902 is not a leap year
# The year 1904 is  a leap year
# The year 1999 is not a leap year
# The year 2000 is  a leap year
# The year 2001 is not a leap year
# The year 2002 is not a leap year
# The year 2003 is not a leap year
# The year 2004 is  a leap year
# The year 2015 is not a leap year
# The year 2016 is  a leap year
# The year 2017 is not a leap year
# The year 2018 is not a leap year
# The year 2019 is not a leap year
# The year 2020 is  a leap year
# The year 2021 is not a leap year