Deleting from sys.modules and re-importing

Question

Accepted Answer

Deleting sys.modules['mymodule'] tells the import system to forget the cached module. The next 'import mymodule' goes back to disk, re-executes the file, and stores a new module object. Here is the critical subtlety: any code that already did 'from mymodule import MyClass' has a direct reference to the old MyClass. That reference is not updated - it still points to the old object. Only code that does 'import mymodule; mymodule.MyClass' after the re-import will see the new version, because it goes through the module object, which is now the new one. This is exactly why hot-reloading in development tools is tricky. 'importlib.reload()' is a slightly safer alternative that mutates the existing module object in-place, but it still doesn't update 'from ... import' references. Knowing this helps you understand why REPL-based workflows sometimes show stale behavior after you edit a file.