[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 14:48:48 CEST 2013

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.


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