Perform a canot pairing of n-length

Cantor pairing.py

import math

'''
Translated from:
    en.wikipedia.org/wiki/Pairing_function, both the pairing
    and upairing functions
'''
def cantor_pairing(x, y):
    return int((((x + y +1) * (x + y)) / 2) + y)


def cantor_unpair(z):
    w = math.floor((math.sqrt(8 * z + 1) - 1) / 2)
    t = (w * w + w) / 2

    # The second part of unpairing
    y = z - t
    x = w - y
    return (int(x), int(y))


'''
Used to perform some tests
'''
def some_test():
    for i in range(10):
        for j in range(10):
            print("*" * 20)

            paired = cantor_pairing(i, j)
            print("pair(%d, %d): %d" %(i, j, paired))

            unpaired = cantor_unpair(paired)
            print("unpair(%d): %s" %(paired, unpaired))

            converted = chr(paired)
            print("Encoded character of %d is %c " %(paired, converted))
            print("Decoded character %c is %d" %(converted, ord(converted)))

            print("*" * 20)
            print("\n")


'''
a and b are the input digits
output should be pair_length characters long, default is 4
'''
def pair(a, b, pair_length = 4):
    # Check that a and b are integers, do not accept
    # alphabetic characters
    if((not isinstance(a, int)) or (not isinstance(b, int))):
        # Should throw an error instead
        return null

    # We've verified the values supplied are integers only
    a = str(a)
    b = str(b)

    if(len(a) > pair_length or len(b) > pair_length):
        # should throw an error or something
        return null

    # The string is in the allowed range, pad any missing values, e.g. if
    # input is 12 pad it to make it 0012 i.e. always 4 characters long
    a = str("0" * (pair_length - len(a))) + a
    b = str("0" * (pair_length - len(b))) + b

    # Where the result of this pairing function will be stored
    result = ""

    # For each character in 
    for i in range(pair_length):
        result += chr(cantor_pairing(int(a[i]), int(b[i])))

    # Return the final result which should be pair_length characters long
    return result


# Reverses the above function
def unpair(s):
    # Explicitlymake sure that s is a string
    s = str(s)

    # the x value
    x = -1

    # the y value
    y = -1

    # For each character in s
    for char in s:
        temp = cantor_unpair(ord(char))

        if x == -1 or y == -1:
            x = temp[0]
            y = temp[1]

        else:
            x = (x * 10) + temp[0]
            y = (y * 10) + temp[1]

    return (int(x), int(y))


if __name__ == "__main__":
    # Uncomment the line below to run some test
    #some_test()

    # Begining of the main thing

    #pairing
    result = pair(9999, 9999)
    print("Paired result is '%s' which is %d characters long " %(result, len(result)))

    # Unpairing
    unpaired_result = unpair(result)
    print("unpaired result ")
    print(unpaired_result)