[Python-Dev] RE: test_sort.py failure (original) (raw)

Raymond Hettinger python at rcn.com
Thu Jul 29 12:06:19 CEST 2004

I want to insist on documented invariants

Absolutely.

but I don't particularly care what they are.

Right. I just wanted to point out an alternative invariant that did not rely on knowledge of the ob_allocated field.

The idea that "list.obitem == NULL implies list.allocated may be lying" is at least as obscure as the invariant that broke, . . . There's no force working toward keeping knowledge of list.allocated confined to the two routines you originally taught about it, unless we believe listobject.c will never be changed again .

Okay. Those good reasons to prefer the invariants you just documented.

> * listassslice() should add a line to maintain them, > * listresize() can drop the test for obitem != NULL, and

Will put these in.

* tpnew needs a custom listnew() establishing the invariants.

> PyTypeGenericNew guarantees to zero-fill all the data space (there's nothing special about list.obitem in this respect -- the generic new has no idea there's a pointer in the struct, it simply zeroes out everything). That establishes the currently documented invariants.

Right. I remembered that after I sent the last note. Will add a comment in list_init so it doesn't get forgotten again.

Raymond

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