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Incremental backup

Project description

A Python class for file comparison and new file backup.

Author: Yu Sun at University of Sydney




When it comes to backing up a large amoumt of data, it is often preferable to only copy the modified and new files, rather than simply coping the whole directory. The AmendmentBackUp (ABU) class provides a simple interface to do that. No dependencies are required apart from the Python 3 standard library.

The design

Say we have two folders, a source folder dir1 which you have your most recent files and a reference folder dir2 which holds some of your previous backup. What the ABU does is to compare all files in dir1 with those in dir2, and copy the files to a third destination folder dst.

A quick example

from AmendmentBackUp import *
abu = AmendmentBackUp(dir1=r"demo/dir1",


Say you have the dir1 and dir2 (along with a dst to copy the files to) with the following tree structures:

dir1 (source, recently updated)
|   file1.txt
|   file2.txt (modified)
|   file3.txt (new)
|       file4.txt
|       file5.txt
|       file6.txt (modified)
\---subfolder3 (new)

dir2 (reference, e.g. a previous backup)
|   file1.txt
|   file2.txt
|   file7.txt
|       file4.txt

dst (destination)

In this case, we want to copy the modified and new file(s) in dir1:


and new folder(s):


You can initiate an ABU object by calling

abu = AmendmentBackUp(dir1=r'path_to/dir1',

By the way, the createDemo() will create a demo folder with structures shown above. After initiation, call the following ABU methods to proceed:

  • Compare files by walking through all files and folders in dir1 and check the existence of the corresponding counterparts in dir2.

    • If negative, it then adds the file or folder to the copy list;

    • If positive, it compares two corresponding files (from dir1 and dir2 respectively, shallow comparison using the time stamp and the file size);

      • If two files don’t match, it will add the file to the copy list;

      • Otherwise, it will continue to the next one.

  • abu.backup(): Copy the files and folders in the copy list.

    • Folders will be copied first. If the parent folder has been copied, any child folder will be skipped;

    • Files will copied next. If the file falls under any folder copied in the previous step, it will be skipped.

  • The metadata of the backup process will be stored in a folder called _abu with a time stamp (year-month-day-hour-minute-second) in the dst folder. These include

- abu_log.txt      Log file
- abu_obj.pickle   ABU object of this backup task
- dir1_tree.txt    Tree structure of dir1 (source)
- dir2_tree.txt    Tree structure of dir2 (reference)
- dst_tree.txt     Tree structure of dst (destination)


Here is the tree structure of dst after the backup:

|   file2.txt
|   file3.txt
|       file6.txt
|       anyfile.txt

If you want to add the files to the previous back dir2, you can simply set dst to dir2.


The ABU is best suited when the source folder dir1 is a natural growth of the reference folder dir2. What natural growth means is that there should not be too much renaming or move of the subfolders from dir2 to dir1. Otherwise, using a version control system is probably a better option since ABU won’t track the history of any folder or file.

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