On 25 July 2012 07:29, Stefan Behnel <stefan...@behnel.de> wrote: > Stefan Behnel, 25.07.2012 07:40: >> Mike Zaletel, 25.07.2012 00:40: >>> --------bug.pyx---------- >>> >>> def foo(): >>> cdef int i >>> cdef int* p1 = [4, 4] >>> cdef int* p2 = [5, 5] >>> >>> print "p1:", >>> for i in range(2): >>> print p1[i], >>> print "\np2:", >>> for i in range(2): >>> print p2[i], >>> >>> ----------------------------- >>> >>> which in Cython 0.17beta1 gives me >>> >>> >>> import bug >>> >>> bug.foo() >>> p1: 5 5 >>> p2: 5 5 >>> >>> >>> while in Cython 0.16 I get >>> >>> >>> import bug >>> >>> bug.foo() >>> p1: 4 4 >>> p2: 5 5 >> >> The problem is that the same (temporary) local array variable is used in >> both cases to build the array, and then only a pointer is assigned, i.e. p1 >> and p2 then point to the same array, which gets overwritten with the new >> values in the second assignment. > > Looking into this some more, the problem arises from the pointer > assignment, because the left side is a pointer variable whereas the right > side is a temp value. Temps aren't really made for an enduring life. Here, > the array temp variable is being freed after the assignment and then > reused. We could fix it by not freeing the temp, or at least by not reusing > it, but the problem is really in the syntax. The LHS should be an array, > not a pointer. > > It broke (and I broke it) when I fixed pointer type comparisons and made > pointer and array types properly hashable. I think it was already subtly > broken before in Py2 and just didn't show because it's sufficiently > unlikely that two equal array types that use the default hash by object > id() end up in the same dict bucket. Only then would the __eq__() > comparison strike to reuse the same temp for both types. > > Stefan > > _______________________________________________ > cython-devel mailing list > cython-devel@python.org > http://mail.python.org/mailman/listinfo/cython-devel
I'm wondering, what was the original motivation to reuse temporaries? I think it leads to more problems than benefits in most cases, all you really care about is clearing up references. Do we ever have C++ stack-allocated object temporaries? Or does it save some stack space (always, or when you take a pointer to the temporary)? _______________________________________________ cython-devel mailing list cython-devel@python.org http://mail.python.org/mailman/listinfo/cython-devel
