06.01.19 13:10, Paul Sokolovsky пише:
Storing None looks superfluous. For example, DELETE_FAST explicitly
stores NULL on delete.
https://github.com/python/cpython/blob/master/Python/ceval.c#L2249
Likewise, for DELETE_NAME/DELETE_GLOBAL, PyObject_DelItem() is
called which translates to:
m->mp_ass_subscript(o, key, (PyObject*)NULL);
So hopefully any compliant mapping implementation actually clears
stored value, not leaving it dangling.
The "store None" behavior can be traced down to introduction of the
"del except target var" behavior back in 2007:
https://github.com/python/cpython/commit/b940e113bf90ff71b0ef57414ea2beea9d2a4bc0#diff-cb296cc5109f5640ff3f6d7198a6abeeR1999
There's no clear explanation why it's done like that, so probably an
artifact of the initial implementation. Note that even
https://github.com/python/cpython/commit/520b7ae27e39d1c77ea74ccd1b184d7cb43f9dcb
which did quite a bunch of refactoring to "except" implementation, and
reformatted this code, otherwise left it in place.
Because there is a reason for such code.
See issue1631942 [1] and the thread with the subject "self-contained
exceptions" on the Python-3000 mailing list [2] for the rationale.
In short, the code
try:
1/0
except Exception as e:
del e
should work.
I do not see a problem with storing None before deleting a variable.
This is not a performance critical code, because it is executed only
when an exception was raised and caught.
[1] https://bugs.python.org/issue1631942
[2] https://mail.python.org/pipermail/python-3000/2007-January/005294.html
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
https://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
