[Python-Dev] Strange artifacts with PEP 3121 and monkey-patching sys.modules (in csv, ElementTree and others)

Stefan Behnel stefan_ml at behnel.de
Sun Aug 11 14:53:59 CEST 2013

Stefan Behnel, 11.08.2013 14:48:
> Antoine Pitrou, 11.08.2013 14:32:
>> On Sun, 11 Aug 2013 14:16:10 +0200 Stefan Behnel wrote:
>>>> We
>>>> just need to devise a convenience API for that (perhaps by allowing to
>>>> create both the subclass *and* instantiate it in a single call).
>>> Right. This conflicts somewhat with the simplified module creation. If the
>>> module loader passed the readily instantiated module instance into the
>>> module init function, then module subtypes don't fit into this scheme anymore.
>>> One more reason why modules shouldn't be special. Essentially, we need an
>>> m_new() and m_init() for them. And the lifetime of the module type would
>>> have to be linked to the (sub-)interpreter, whereas the lifetime of the
>>> module instance would be determined by whoever uses the module and/or
>>> decides to unload/reload it.
>> It may be simpler if the only strong reference to the module type is in
>> the module instance itself. Successive module initializations would get
>> different types, but that shouldn't be a problem in practice.
> Agreed. Then the module instance would just be the only instance of a new
> type that gets created each time the module initialised. Even if module
> subtypes were to become common place once they are generally supported
> (because they're the easiest way to store per-module state efficiently),
> module reinitialisation should be rare enough to just buy them with a new
> type for each. The size of the complete module state+dict will almost
> always outweigh the size of the one additional type by factors.

BTW, this already suggests a simple module initialisation interface. The
extension module would expose a function that returns a module type, and
the loader/importer would then simply instantiate that. Nothing else is needed.


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