[Python-Dev] PySet API
raymond.hettinger at verizon.net
Sun Mar 26 18:43:35 CEST 2006
> Speaking as a person who does relatively little C programming, I don't
> see much difference between them. The first example is more Pythonic --
> for Python. I agree with Barry that it's not much of a virtue for C
It was a trick question. Everyone is supposed to be attracted to the _next
version because it is shorter, faster, and takes less ref counting management.
However, the _next version has a hard-to-find bug. The call to PyObject_Hash()
can trigger arbitrary Python code and possibly mutate the table, leaving
pointers to invalid memory addresses. It would likely take Armin less than five
minutes to write a pure Python crasher for the code. And THAT is why
PySet_Next() should never come into being.
The iterator form is more duck-typable and re-usable than the set specific _next
version, but the example was chosen to take that issue off of the table and just
focus on mutation issues.
> However, I do have one nitpick with both your examples; I don't know
> whether this is an artifact of them being examples:
>> hash ^= h * 3644798167;
> Seems to me that magic numbers like this need to be made constants and
> explained with a comment
FWIW, the actual code does have comments. I stripped them out of the posting
because they weren't relevant to the code comparison.
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