While you're right it is an easy to make mistake with decorators, I don't think the issue is global mutable state as much as uncontrolled mutable state, especially if used against singleton.

Typically, doing this:

    @register
    def foo():
    ….

is bad, but this is much better:

    @registry.register
    def foo():
    …

if registry is a global object that is not a singleton. In that case, you can easily use distinct registries (for testing, etc…) and this is not much of an issue in practice. Another way of doing this kind of things is to post_pone the registration, with the decorator just labelling things:

    @register
    def foo():
    …

    def register(f):
        return WrappedFunc(f)

and then build an explicit list of modules being imported, and look for every instance of WrappedFunc in that module locals(). I use this in my own packaging project where people can define multiple python scripts that hook into different stages of the packaging.