Python doesn't re-read a function's source code from the filesystem every time it calls it, and that would be a bad idea in general since you'd inadvertently cr

Python doesn't re-read a function's source code from the filesystem every time it calls it, and that would be a bad idea in general since you'd inadvertently crash your running programs during development. This watches for changes on the filesystem and injects them into the running program as well as it can, basically keeping the current program state but with new behaviour. This is kind of a footgun and there are many changes you can make that will crash or ruin the process, but if you're aware of the limitations it can be pretty useful.