Manipulating sets from the 2.4 C API?

[Dave Opstad]

I just looked through the Python/C API reference for 2.4.3 and didn't
see anything about using sets. I'd been expecting things like PySet_New,
PySet_Check etc.

If I want to handle sets should I just use a dictionary's keys and
ignore the values, or is there some more explicit set support somewhere
I'm not seeing?

Thanks,
Dave Opstad

[Jack Diederich]

On Tue, Apr 11, 2006 at 09:29:10AM -0700, Dave Opstad wrote:

I just looked through the Python/C API reference for 2.4.3 and didn't
see anything about using sets. I'd been expecting things like PySet_New,
PySet_Check etc.
There is a public C API starting in 2.5, the progression for sets was
pure-python in 2.3, C in 2.4, and polished in 2.5 after it was better
understood how people use them. If Hettinger is around he'll correct me
if that explanation is off.
If I want to handle sets should I just use a dictionary's keys and
ignore the values, or is there some more explicit set support somewhere
I'm not seeing?

There are people that use sets from C-code but I don't know if they use
the slotted methods, the 2.5 version, or a special build.

-Jack

[Martin v. Löwis]

Dave Opstad wrote:

If I want to handle sets should I just use a dictionary's keys and
ignore the values, or is there some more explicit set support somewhere
I'm not seeing?

Indeed, there is. To create a new set, do

PyObject_Call(PySet_Type, "");

To, say, invoke the add method, do

PyObject_CallMethod(s, "add", "O", o);

HTH,
Martin

[Felipe Almeida Lessa]

Em Ter, 2006-04-11 Ã*s 18:55 +0200, "Martin v. Löwis" escreveu:

Dave Opstad wrote:

If I want to handle sets should I just use a dictionary's keys and
ignore the values, or is there some more explicit set support somewhere
I'm not seeing?

Indeed, there is. To create a new set, do

PyObject_Call(PySet_Type, "");

To, say, invoke the add method, do

PyObject_CallMethod(s, "add", "O", o);

I don't know much about the C API, but I'll ask anyway: the methods,
say, PySet, would be included for clarity/brevity or for performance
reasons?

--
Felipe.

[Raymond Hettinger]

Dave Opstad wrote:

I just looked through the Python/C API reference for 2.4.3 and didn't
see anything about using sets. I'd been expecting things like PySet_New,
PySet_Check etc.
In Py2.4, there was not a custom set C API because the module was still
ungoing significant development. For 2.4, the best way to access sets
from C is to use the abstract API:

s=PyObject_CallObject(PySet_Type, NULL) // s=set()
PyObject_TypeCheck(o, &PySet_Type) // isinstance(o, set)
PyObject_GetIter(s) // iter(s)
PyObject_Hash(f) // hash of frozenset
PyObject_Length(s) // len(s)
PyNumber_Subtract(s,t) // s - t
PyObject_CallMethod(s, "pop", NULL) // s.pop()

If I want to handle sets should I just use a dictionary's keys and
ignore the values, or is there some more explicit set support somewhere
I'm not seeing?

In Py2.4, set objects are based on dictionaries so the performance is
about the same, so the only advantage of using set objects instead of
dictionaries is that they provide methods like union, intersection, etc
which are not defined for dictionaries.

In Py2.5, set objects are no longer based on dictionaries and tend to
have better speed/space performance than equivalent dictionary code.
There is also a more full-blown C API including PySet_New(),
PySet_Size(), PySet_Add(), PySet_Contains(), ...