Python implementation of Hamming (7,4) encoding.

h74-encode.py

# Hamming (7,4) Coding
#
# Reads binary stream from standard input and outputs Hamming (7,4) encoded
# version to standard output.
#
# USAGE: python h74-encode.py
#
# EXAMPLE:
#      $ echo "0001" | python h74-encode.py
#      1000101
#
# AUTHOR: Mark Reid <[email protected]>
# CREATED: 2013-10-21

import sys

K = 4
def encode(s):
    """Read in K=4 bits at a time and write out those plus parity bits"""
    while len(s) >= K:
        nybble = s[0:K]
        sys.stdout.write(hamming(nybble))
        s = s[K:]

def hamming(bits):
    """Return given 4 bits plus parity bits for bits (1,2,3), (2,3,4) and (1,3,4)"""
    t1 = parity(bits, [0,1,2])
    t2 = parity(bits, [1,2,3])
    t3 = parity(bits, [0,2,3])
    return bits + t1 + t2 + t3 

def parity(s, indicies):
    """Compute the parity bit for the given string s and indicies"""
    sub = ""
    for i in indicies:
        sub += s[i]
    return str(str.count(sub, "1") % 2) 

###################################################################################
# Main

if __name__ == "__main__":
    input_string = sys.stdin.read().strip()
    encode(input_string)

can you please explain the parity function

The parity function, as written, is taking the 3 bits (one from each of the indices), concatenating them into a string, and then counting the number of 1's in that resultant string. If the number of 1's mod 2 is the parity bit.

When sub = 101 then str.count() will be 2, and 2 % 2 = 0, so parity() returns 0. If sub = 111 or 010 (str.count() = 3 or 1) or anything else with an odd # of 1's then str.count() will return 1 as parity.

Why not implement (8, 4) hamming code?

Hi!
when trying to process it, it gives wrong answer..
I've checked it myself manually

It's wrong.

is it ok?