See Self and Smalltalk for such kind of highly dynamic environment with code being loaded, and completely changing the running image on the fly.

Yet both languages are on the genesis of modern JIT compilers, going beyond what was already being done for Lisps, Prolog, BASIC.

> JavaScript also has monkey-patching, and it's also very common. E.g. SolidJS replaces objects with dependency-tracking proxies.

And the proxies make it slow as Python. Plain objects cannot suddenly become proxies, so the runtime can treat them as a special case.