[Python-Dev] PEP 443 - Single-dispatch generic functions (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Fri May 24 14:37:26 CEST 2013

On Fri, May 24, 2013 at 10:22 PM, Ronan Lamy <ronan.lamy at gmail.com> wrote:

Raise a ValueError, maybe? In that case, there needs to be a way to force the overriding when it is explicitly desired. One way would be to allow unregistering implementations: overriding is then done by unregistering the old implementation before defining the new one. This is a bit cumbersome, which IMHO is a good thing for an operation that is just as disruptive as monkey-patching a class or a module.

If you're registering an implementation for a type you didn't define on a generic function you didn't define, it's exactly as disruptive as monkey-patching. Note that the PEP proposes giving exactly as much of a runtime warning about overwriting a registration as we do about monkeypatching: none.

The two cases are exactly analagous: you can do it, you don't get a warning if you do it, but it you do it implicitly as a side effect of import then you will have developers cursing your name. So don't do that, put it in a function that people can call if they want to register your implementations (along the lines of gevent.monkey).

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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