[Python-Dev] PEP 443 - Single-dispatch generic functions

Ronan Lamy ronan.lamy at gmail.com
Fri May 24 14:22:19 CEST 2013

2013/5/24 Ethan Furman <ethan at stoneleaf.us>

> On 05/23/2013 02:02 PM, Ronan Lamy wrote:
>> 2013/5/23 Łukasz Langa <lukasz at langa.pl <mailto:lukasz at langa.pl>>
>>     On 23 maj 2013, at 20:13, Éric Araujo <merwok at netwok.org <mailto:
>> merwok at netwok.org>> wrote:
>>     > Question: what happens if two functions (say in two different
>> modules)
>>     > are registered for the same type?
>>     Last one wins. Just like with assigning names in a scope, defining
>> methods
>>     in a class or overriding them in a subclass.
>> This is a serious annoyance, considering that there are several places
>> where a large library can reasonably define the
>> implementations (i.e. with the class, with the function, or in some
>> utility module). Note that in contrast with the case
>> of functions in a module or methods in a class, linting tools cannot be
>> expected to detect a duplication between
>> functions with different names defined in different modules.
> What would you suggest happen in this case?

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.
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