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Python implementation of Hamming (7,4) encoding.
# 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 <mark.reid@anu.edu.au>
# 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)
@SaloniGandhi

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@SaloniGandhi SaloniGandhi commented Mar 30, 2016

can you please explain the parity function

@apraetor

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@apraetor apraetor commented Apr 6, 2016

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.

@FluxIX

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@FluxIX FluxIX commented Apr 28, 2016

Why not implement (8, 4) hamming code?

@maliwari

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@maliwari maliwari commented Mar 3, 2017

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

@bicycleprincess

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@bicycleprincess bicycleprincess commented Mar 31, 2017

It's wrong.

@JacekPiotrowski235849

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@JacekPiotrowski235849 JacekPiotrowski235849 commented Apr 6, 2018

is it ok?

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