Display diff between two commits.

bdiff.py

#!/usr/bin/env python
import sys, subprocess, os

TOOLS = ['bcompare', 'meld']
HEAD = 'HEAD'
TMP = '/tmp/'

execute = lambda command: subprocess.check_output(command)
which = lambda tool: execute(['which', tool]).strip()

def getTool():
	for tool in TOOLS:
		try:
			out = which(tool)
			if tool in out:
				return tool
		except subprocess.CalledProcessError:
			pass
	return None

def printUsageAndExit():
	print 'Usage: python bdiff.py <project> <commit_one> <commit_two>'
	print 'Example: python bdiff.py <project> 0 1'
	print 'Example: python bdiff.py <project> fhejk7fe d78ewg9we'
	print 'Example: python bdiff.py <project> 0 d78ewg9we'
	print 'Example: python bdiff.py <project> HEAD d78ewg9we'
	print 'Example: python bdiff.py <project> HEAD-4 87'
	sys.exit(0)

def revParse(name, position):
	if '-' in position:
		position.replace('-', '~')
	command = ['git', '-C', name, 'rev-parse', position]
	return execute(command).strip()

def getCommitId(name, position):
	index = -1;
	command = ['git', '-C', name, 'log', '--pretty=format:"%h"', '--abbrev=7']
	reverse = ['--reverse']
	if position == HEAD:
		return revParse(name, position)
	elif HEAD in position and ('-' in position or '~' in position):
		try:
			return revParse(name, position)
		except ValueError:
			print "Error in parsing commit ids!"
			sys.exit(0)
	elif HEAD in position:
		print "Error in parsing commit ids!"
		sys.exit(-1)
	elif '-' in position:
		commitid = position.split()[0][:7]
		index = execute(command).splitlines().index(commitid)
		try:
			index -= int(position.split()[1])
		except ValueError:
			print "Unable to paser the input!"
			sys.exit(-1)
	elif position.isdigit():
		command.extend(reverse)
		index = int(position)
	else:
		return position
	if index >= 0:
		logs = execute(command).splitlines()
		return logs[index].strip()
	else: return None

dir_name = lambda commit: (commit if commit else '0')

tmp = lambda name: (TMP + dir_name(name))

def validate(name, commit):
	if not commit:
		print "Nothing to do, exit!"
		return False
	try:
		if commit:
			execute(['git', '-C', name, 'cat-file', '-t', commit])
	except subprocess.CalledProcessError:
		return False
	return True

cleanup = lambda commit: execute(['rm', '-rf', tmp(commit)])

def checkoutCommit(name, commit):
	if commit:
		execute(['git', 'clone', name, tmp(commit)])
		execute(['git', '-C', tmp(commit), 'checkout', commit])
	else:
		execute(['mkdir', tmp('0')])

def compare(tool, commit1, commit2):
		execute([tool, tmp(commit1), tmp(commit2)])

def parseOpt():
	if len(sys.argv) is 2:
		return os.getcwd(), sys.argv[1]+'-1', sys.argv[1]
	elif len(sys.argv) is 3:
		return os.getcwd(), sys.argv[1], sys.argv[2]
	elif len(sys.argv) is 4:
		return sys.argv[1], sys.argv[2], sys.argv[3]
	else: printUsageAndExit()

if __name__ == '__main__':
	tool = getTool()
	if not tool:
		print "No GUI diff tools, install bcompare or meld"
		sys.exit(0)

	name, first, second = parseOpt()

	commit1, commit2 = getCommitId(name, first), getCommitId(name, second)

	if validate(name, commit1) and validate(name, commit2) is False:
		sys.exit(0)

	cleanup(commit1), cleanup(commit2)

	try:
		checkoutCommit(name, commit1), checkoutCommit(name, commit2)
		compare(tool, commit1, commit2)
	except KeyboardInterrupt:
		pass
	finally:
		cleanup(commit1), cleanup(commit2)
	sys.exit(0)

It is assumed 'meld' is installed:
local_git_dir$ bdiff.py . 15d3c2ec3d007a5f0a6387a4998dc6fbcd9d93f5 c182600f5ff2491964af59c32933efa73575949d
or
local_git_dir$ bdiff.py . HEAD c182600f5ff2491964af59c32933efa73575949d
or
$ bdiff.py local_git_dir HEAD c182600f5ff2491964af59c32933efa73575949d

The following will all error out (even after replacing "catch" with "except"):
$ bdiff.py local_git_dir 0 1
$ bdiff.py local_git_dir HEAD HEAD-1