merge.py

#!/usr/bin/env python
import sys, difflib

# The version of the file from the common ancestor of the two branches.
# This constitutes the 'base' version of the file.
ancestor = open(sys.argv[1],'r').readlines()

# The version of the file at the HEAD of the current branch.
# The result of the merge should be left in this file by overwriting it.
current = open(sys.argv[2],'r').readlines()

# The version of the file at the HEAD of the other branch.
other = open(sys.argv[3],'r').readlines()

def get_difference(one,two):
    d = difflib.Differ()
    diff = d.compare(one,two)
    added_lines = []
    for line in diff:
            if line.startswith('+ '):
                if not line.strip() == '+ <<<<<<< HEAD':
                   added_lines.append(line[2:])
            elif line.startswith('-  '):
                raise DiffError("remove is not supported")
    return added_lines

lines = get_difference(ancestor,other)

print(lines)

while not current[-1].strip():
    current = current[:-1]
current.append("\n")
while not lines[0].strip():
    lines = lines[1:]

current.extend(lines)

f = open(sys.argv[2],'w')
f.writelines(current)
f.close()