Julien Palard added the comment:
Problem looks mainly due to the __setattr__ done on a different type than the
getattr, and the cache of PyType_Lookup:
- type_setattro will be called with Foo, "x", and the value to set
- type_getattro will be called with FooProxy, "x"
The timeline (with my weird_without_interactive.py) is:
- type_setattro is called on Foo for attr "x" with the instance of Bar
- type_getattro is called on FooProxy for attr "x" (the `proxy.x` line)
During this type_getattro, the instance of Bar is cached in PyType_Lookup
for (FooProxy, "x")
- type_setattro is called on Foo for attr "x" with the value 0
During this call, insertdict will legitimately call DECREF on the Bar
instance, which is deleted
- type_getattro is called on FooProxy with attr "x" for the print()
During this call, PyType_Lookup will cache hit for (FooProxy, x) with the
old reference to the instance of Bar
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Python tracker <[email protected]>
<http://bugs.python.org/issue28866>
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