def yum_groupinstall(packages, excludelist = [], roles = " ".join([item.lower() for item in get_roles()])):
        print '@Installing packages with groupinstall'
        regex1 = re.compile('^Error: .+ conflicts with ')
        excludes = ' '.join(["--exclude=%s" % exclude for exclude in excludelist])

        (stdin, output) = os.popen4("/usr/bin/yum %s groupinstall %s" % (excludes, roles))
        for line in output.readlines():
                print line.strip()  ## TODO:  remove
                if line.startswith('Error: ') or line.endswith(' is not signed') or regex1.match(line) != None:
                        raise Exception
        return

def yum_chunkinstall(packages, excludelist = [], chunksize = 15):
        print '@Installing packages chunkwise'

        excludes = ' '.join(["--exclude=%s" % exclude for exclude in excludelist])
        regex1 = re.compile('^Error: .+ conflicts with ')
        total = len(packages)/chunksize
        for chunk in range(len(packages)/chunksize):
                chunkstart = chunksize * chunk
                chunkend = chunkstart + chunksize
                print "@Installing piece %s of %s" % (chunk + 1, total)
                piece = ' '.join(packages[chunkstart:chunkend])
                print piece
                messages = []
                blocks = []
                (stdin, output) = os.popen4("/usr/bin/yum -y %s install %s" % (excludes, piece))
                for line in output.readlines():
                        print "@%s" % line.strip()
                        messages.append(line.strip())
                        if line.startswith('Error: ') or line.endswith(' is not signed') or regex1.match(line) != None:
                                print '@Chunkwise install failed'
#                               try:  ## TODO:  reinstate try block
                                print "@@A %s" % blocks  ## diagnostic
                                newblocks = yum_pruneinstall(packages[chunkstart:chunkend], excludelist, messages)
                                print "@@C %s" % newblocks  ## diagnostic
                                blocks.extend(newblocks)
                                print "@@D"  ## diagnostic
                                blocks = list(set(blocks))
                                print "@@E"  ## diagnostic
                                excludelist.extend(blocks)
                                print "@@F"  ## diagnostic
                                excludelist = list(set(excludelist))
                                print "@@G"  ## diagnostic
#                               except:
#                                       print "@Install failed for packages: %s" % piece
#                                       blocks.extend(packages[chunkstart:chunkend])
        update_log()
        return blocks

def yum_pruneinstall(packages, blocks = [], messages = [], iteration = 0, maxiterations = 16):
        print "@Pruning blocks (try %s of %s)" % (iteration, maxiterations)

        regex1 = re.compile('^Error: .+ conflicts with ')
        errored = False
        piece = ' '.join(packages)
        print piece

        for line in messages:
                if line.startswith('Error: Missing Dependency: '):  # Missing dependencies
                        blocks.append(line.split()[-1])
                        errored = True
                elif line.endswith(' is not signed'):  # Unsigned packages
                        blocks.append(line.split('.', 1)[0].split('-', 1)[-1].split()[1])
                        errored = True
                elif regex1.match(line) != None:  # Conflicting packages
                        blocks.append(line.split()[1])
                        errored = True
        if not errored:
                update_log()
                print "@Piece succeeded!"  ## TODO:  remove
                print "@@B %s" % blocks  ## diagnostic
                return blocks
        else:
                if iteration == maxiterations:
                        print '@Giving up'  ## TODO:  remove
                        raise Exception
                # Remove duplicates
                blocks = list(set(blocks))
                print "#Blocks:  %s" % blocks  ## TODO:  remove

        # Run yum again and restart
        excludes = ' '.join(['--exclude=%s' % block for block in blocks])
        messages = []
        (stdin, output) = os.popen4("/usr/bin/yum -y %s install %s" % (excludes, piece))
        for line in output.readlines():
                messages.append(line.strip())
                print "@%s" % line.strip()  ## TODO:  remove
        yum_pruneinstall(packages, blocks, messages, iteration + 1)