tp_new, tp_alloc, tp_init

[Michael Hennebry]

I've been reading about writing extension types in C and am rather
fuzzy about the relationship between tp_new, tp_alloc and tp_init.
Most especially, why tp_new? It seems to me that tp_alloc and tp_init
would be sufficient.

Most of my reading has been in the Noddy and Shoddy portions of
docs.python.,org .

 

[Gregory Ewing]

I've been reading about writing extension types in C and am rather
fuzzy about the relationship between tp_new, tp_alloc and tp_init.
Most especially, why tp_new? It seems to me that tp_alloc and tp_init
would be sufficient.

tp_new and tp_init correspond to the Python methods
__new__ and __init__, and they're separated for the
same reasons they are in Python.

tp_alloc is separate because it allows a type to
use a custom memory allocator without disturbing the
rest of the initialisation mechanism.