[Python-Dev] frozenset C API?
janssen at parc.com
Tue Sep 4 21:31:09 CEST 2007
Raymond, thanks for the note.
> You can create a frozenset from any iterable using PyFrozenSet_New().
> If you don't have an iterable and want to build-up the frozenset one element at a time, the approach is to create a regular set (or some other mutable container), add to it, then convert it to a frozenset when you're done:
> s = PySet_New(NULL);
> PySet_Add(s, obj1);
> PySet_Add(s, obj2);
> PySet_Add(s, obj3);
> f = PyFrozenSet_New(s);
This is essentially the same thing I mentioned, except using a set
instead of a list as the iterable.
I'm just a tad annoyed at the fact that I know at set creation time
exactly how many elements it's going to have, and this procedure
strikes me as a somewhat inefficient way to create that set. Just
tickles my "C inefficiency" funnybone a bit :-).
> The API you propose doesn't work because sets and frozensets are not
> indexed like tuples and lists. Accordingly, sets and frozensets have
> a C API that is more like dictionaries. Since dictionaries are not
> indexable, they also cannot have an API like the one you propose:
> PyDict_NEW(int) => PySetObject *
> PyDict_SET_ITEM(s, index, key, value)
Didn't really mean to propose "PyDict_SET_ITEM(s, index, key, value)",
should have been
PyDict_SET_ITEM(s, index, value)
But your point is still well taken. How about this one, though:
PyDict_NEW(int) => PySetObject *
ADD would just stick value in the next empty slot (and steal its
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