Cython calls ExtType.__init__() as Python function

[robertwb]

When subclasses of extension types call the __init__() method of their supertype, Cython generates code that looks up the "__init__" attribute of the instance and then calls it through Python using arg tuple/kwargs. This is because the special __init__() method ("tp_init" slot) uses this call signature.

Cython should recognise calls to this method and at least call it directly.

In the (presumably very common) case that the arguments do not use starargs, a more advanced approach would be to split the __init__() method into an internal plain C-function replacement and a tp_init wrapper, and then call the internal function directly, without doing any tuple packing etc. Not sure if it's worth it, though, as the call is already preceded by an (expensive) object allocation.

[gfurnish]

One of the first things I do is make my own c wrappers for creating objects. Even with the expensive new call the savings it noticeable.

[scoder]

The same idea is reported in #141. This should use cpdef semantics.

[scoder]

The same applies to other special methods like __call__. (noted here to close #141 as a duplicate)