[Python-Dev] Identifier API (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Sat Oct 15 13:45:26 CEST 2011

PyObject *tmp; Pyidentifier(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 PyObjectCallMethod() 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

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