Are you tired of constantly having to update your code every time a new version of Python comes out?

Now, let me start by saying that this is not a perfect solution. It can’t magically transform your Python 3 code into flawless Python 2 equivalents without any issues whatsoever. But hey, at least you won’t have to spend hours manually fixing every single line of code!

So how does it work? Well, lib3to2 is a set of fixers that are intended to backport your shiny new Python 3 code into the ancient and outdated world of Python 2. The final target version is the latest release in the Python 2.x branch (which is currently 2.7).

But wait, you might be thinking what about all those fancy features that are only available in Python 3? Don’t worry, lib3to2 tries to fix as many of these as possible! However, there are some subtle and not-so-subtle differences between the two languages that cannot be easily transformed.

For example, let’s say you have a function that uses f-strings (which were introduced in Python 3.6). Lib3to2 will try to convert it into an equivalent using string formatting or some other method. But if your code relies heavily on these features, there might be issues that cannot be fixed automatically.

So what’s the best way to use lib3to2? Well, you can run “lib3to2” from the command line and it will convert stdin (or files/directories) into a unified diff-formatted patch on standard output. If you want to write back converted files, just add the “-w” option.

But be warned this tool is not perfect! It might produce working Python 2 code or warn about why it did not. Any other behavior is a bug and should be reported immediately. And since lib3to2’s fixers are somewhat well-tested individually, but there is no testing done on interactions between multiple fixers, most of the bugs in the future will likely be found there.

So if you want to use lib3to2 for your Python 3 code, make sure that it’s thoroughly tested and avoid embedding backwards-incompatible code too deeply into your project. And remember this tool is not a complete solution for directly backporting Python 3 code!