Vitja Makarov, 05.07.2011 10:37:
2011/7/5 Stefan Behnel:
IMO, the main reason for the heuristic is to prevent class objects from
being kept alive by their methods, except for the single case where super()
is used. Keeping a class alive just because one of its methods is still used
somewhere can be very costly, depending on the content of the class dict. It
also creates a reference cycle, which is another costly thing in CPython as
it requires a GC run over the whole class dict to get cleaned up.
The situation for modules is at least slightly different, as modules do not
tend to get unloaded, so there's always a reference to them from
sys.modules. If that ever gets removed, it's really ok if it takes time to
clean things up.
Yes, but I hope that classes are rarely deleted.
And I'm afraid that we can't avoid cycles when implementing __class__
for pure-python classes.
As I said, it's fine if super() is used, but not otherwise. Basically,
no-args super() is just a shortcut for "super(TheClass, self)", with the
difference that the long form looks up the name at runtime, whereas the
short form keeps a reference to the type at module setup time. So, both
need the class at runtime, but have different characteristics otherwise.
(but if the code is not using super(), there is no need to have the methods
own a reference to their class)
Stefan
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