[Python-Dev] Identifier API

["Martin v. Löwis"]

>> PyObject *tmp;
>> Py_identifier(update);

> As I understand it, the macro expands to both the ID variable
> declaration and the init-at-first-call code, right?

No. The variable will only get static initialization with the
char*. The initialization on first call (of the PyObject*) happens
in the helper functions, such as PyObject_GetAttrId.

> I'm not sure how often users will need more than one identifier in a function

That's actually fairly common.

> Also note that existing code needs to be changed in order to take
> advantage of this. It might be possible to optimise
> PyObject_CallMethod() internally by making the lookup either reuse a
> number of cached Python strings, or by supporting a lookup of char*
> values in a dict *somehow*. However, this appears to be substantially
> more involved than just moving a smaller burden on the users.

I think this would have to hash the string in any case, since keying
by char* pointer value cannot work (there might be a different string
at the same memory the next time). So even if this could side-step
many of the steps, you'd keep at least one iteration over the
characters; if this is hashing, you actually need two iterations
(the second one to determine whether it's the right string).
The Py_IDENTIFIER API can do the lookup in constant time for all
but the first call.

Regards,
Martin