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Show HN: Modshim – A new alternative to monkey-patching in Python

(github.com)
107 points joouha | 1 comments | 16 Oct 25 11:17 UTC | HN request time: 0.276s | source

I've invented a new alternative to forking / vendoring / monkey-patching packages in Python.

It's a bit like OverlayFS for Python modules - it allows you write modifications for a target module (lower) in a new module (upper), and have these combined in a new virtual module (mount).

It works by rewriting imports using AST transformations, then running both the lower and upper module's code in the new Python module.

This prevents polluting the global namespace when monkey-patching, and means if you want to make changes to a third-party package, you don't have to take on the maintenance burden of forking, you can package and distribute just your changes.

1. afarviral ◴[22 Oct 25 11:38 UTC] No.45667582[source]▶
This is interesting, and I'll try to remember to give this a go next time I'm tempted to patch something from the standard library, but...

The README mentions 3 scenarios that this might be preferred over, but not the fourth which I regularly do: Create my own functions/classes that are composed from the unchanged modules. E.g. a request_with_retries function which adds retry logic to requests without the need to monkey patch. I regularly use decorators as well to add things like retries.

For more complex scenarios Modshim might win out, as mentioned in the understated section of the README "Benefits of this Approach":

> Internal Reference Rewriting: This example demonstrates modshim's most powerful feature. By replacing requests.sessions.Session, we automatically upgraded top-level functions like requests.get() because their internal references to Session are redirected to our new class.

> Preservation of the Original Module: The original requests package is not altered. Code in other parts of an application that imports requests directly will continue to use the original Session object without any retry logic, preventing unintended side-effects.

What I think this means is Modshim lets you really get in to the guts of a module (monkey-patch style, giving you god-like powers), while limiting the damage.