A tool for generating a visual comparison of two Python source code files.
TODO: put some images here!
You'll need Python3 with PIL, and if you want to use the GUI you'll need the TK bindings for PIL. Furthermore, if you want to save images to file, you'll need matplotlib. If you're running on Ubuntu, try this:
sudo apt-get install python3-pil.imagetk
pip3 install matplotlib
On Mac, first make sure you're running Python version 3.7 (as versions 3.6 and earlier have a bug in TK which prevents the scroll events from being processed correctly), and then:
pip3 install pillow
pip3 install matplotlib
If you're running a different OS, good luck (and if you get it to work, please either file an issue telling us to update the documentation with what you did, or update it yourself and send us a pull request!).
You can clone this repository in the usual way:
git clone https://github.com/keyme/visual-diff.git
The short version: run visual_diff.py --help for info.
The main program is visual_diff.py. You can either specify 1 or 2 different
filenames containing Python code as arguments to it. With 2 files, it compares
one to the other; with only 1 file it compares the file to itself.
Each file is treated as a sequence of Python tokens. A token is the smallest semantic piece of a program; tokens include keywords like "if" and "for", parentheses, variable names, indentation changes, etc. We then generate an image, in which the pixel in row i and column j is set if the ith token from the first file and the jth token from the second file are equal. All strings are considered equal regardless of their contents; all numbers are considered equal, too.
If you specify the --gui option (and have the TK bindings for PIL installed),
a graphical user interface will open up in which you can explore the image. Use
the scroll wheel to zoom in and out, click-and-drag to pan around, and mouse
around the image to explore the code. Quit with control-Q or control-W. When
the GUI is finished, the intention is to have it be very similar to Google
Maps, OpenStreetMap, or other map exploration interfaces.
If you don't specify --gui, the image will be saved to file. By default it
goes in output.png, but you can specify a different place to put it with the
-o option.
Don't run this on very large files! It can take up all your RAM trying to write the image to disk or display it to the screen and freeze your whole system. As a quick estimate, if you have a 1000 line file with 10 tokens per line, the resulting image will be 100 megapixels, which can be uncomfortably large.
There are plans to make the GUI not have these problems. but for the moment, it's still an issue. Similarly, it would be neat if we could save large images without falling over (or at least give some sort of a warning and refuse to continue on unless the user explicitly said it was okay), but that isn't built yet, either.
Finding code that has been copied and pasted or is otherwise similar enough to consider refactoring. This is the main use case of this code. These show up as diagonal lines in the image. TODO: give example images and discuss in more detail
- Finding students who are cheating on their homework by copying and pasting
code from each other. There are better tools for this task, but
visual_diffis better than nothing. - Cheating on homework by making sure that the code you have copied and pasted has been modified enough that it no longer looks copied and pasted.
This code was predominantly written by Alan Davidson ([email protected]). He got the idea from a talk he saw at DEFCON 2006, in which Dan Kaminsky showed a very similar tool he had built to compare binaries built from the same source code using different compilers. Here are slides he made for a very similar talk at SchmooCon 2007 (start around slide 45).