Backup Directory in Python

#!/usr/bin/env python

# Backup files - As published in Python Cookbook
# by O'Reilly with some bug-fixes.

# Credit: Anand Pillai, Tiago Henriques, Mario Ruggier
import sys
import os
import shutil
import filecmp

MAXVERSIONS = 100
BAKFOLDER = '.bak'


def backup_files(tree_top, bakdir_name=BAKFOLDER):
    """ Directory back up function. Takes the top-level
    directory and an optional backup folder name as arguments.
    By default the backup folder is a folder named '.bak' created
    inside the folder which is backed up. If another directory
    path is passed as value of this argument, the backup versions
    are created inside that directory instead. Maximum of
    'MAXVERSIONS' simultaneous versions can be maintained

    Example usage
    -------------

    The command
    $ python backup.py ~/programs

    will create backups of every file inside ~/programs
    inside sub-directories named '.bak' inside each folder.
    For example, the backups of files inside ~/programs will
    be found in ~/programs/.bak, the backup of files inside
    ~/programs/python in ~/programs/python/.bak etc.

    The command
    $ python backup.py ~/programs ~/backups

    will create backups of every file inside ~/backups/programs
    folder. No .bak folder is created. Instead backups of
    files in ~/programs will be inside ~/backups/programs,
    backups of files in ~/programs/python will be inside
    ~/backups/programs/python etc.

    """

    top_dir = os.path.basename(tree_top)
    tree_top += os.sep

    for dir, subdirs, files in os.walk(tree_top):

        if os.path.isabs(bakdir_name):
            relpath = dir.replace(tree_top, '')
            backup_dir = os.path.join(bakdir_name, top_dir, relpath)
        else:
            backup_dir = os.path.join(dir, bakdir_name)

        if not os.path.exists(backup_dir):
            os.makedirs(backup_dir)

        # To avoid recursing into sub-directories
        subdirs[:] = [d for d in subdirs if d != bakdir_name]
        for f in files:
            filepath = os.path.join(dir, f)
            destpath = os.path.join(backup_dir, f)
            # Check existence of previous versions
            for index in xrange(MAXVERSIONS):
                backup = '%s.%2.2d' % (destpath, index)
                abspath = os.path.abspath(filepath)

                if index > 0:
                    # No need to backup if file and last version
                    # are identical
                    old_backup = '%s.%2.2d' % (destpath, index-1)
                    if not os.path.exists(old_backup):
                        break
                    abspath = os.path.abspath(old_backup)

                    try:
                        if os.path.isfile(abspath) and filecmp.cmp(abspath, filepath, shallow=False):
                            continue
                    except OSError:
                        pass

                try:
                    if not os.path.exists(backup):
                        print 'Copying %s to %s...' % (filepath, backup)
                        shutil.copy(filepath, backup)
                except (OSError, IOError), e:
                    pass


if __name__ == "__main__":
    if len(sys.argv) < 2:
        sys.exit("Usage: %s [directory] [backup directory]" % sys.argv[0])

    tree_top = os.path.abspath(
        os.path.expanduser(os.path.expandvars(sys.argv[1])))

    if len(sys.argv) >= 3:
        bakfolder = os.path.abspath(
            os.path.expanduser(os.path.expandvars(sys.argv[2])))
    else:
        bakfolder = BAKFOLDER

    if os.path.isdir(tree_top):
        backup_files(tree_top, bakfolder)