Cython: Inline Function not pure C

Question

I have the following inline function for Cython

cpdef inline int c_rate2recs_2(int maxNN,int idx):
  cdef int out=idx%maxNN
  return out

However this translates into

/* 
 *   return out
 * 
 * cpdef inline int c_rate2recs_2(int maxNN,int idx):             # <<<<<<<<<<<<<<
 *   cdef int out=idx%maxNN
 *   return out
 */

static PyObject *__pyx_pw_6kmc_cy_5c_rate2recs_2(PyObject *__pyx_self, PyObject *__pyx_args, PyObject *__pyx_kwds); /*proto*/
static CYTHON_INLINE int __pyx_f_6kmc_cy_c_rate2recs_2(int __pyx_v_maxNN, int __pyx_v_idx, CYTHON_UNUSED int __pyx_skip_dispatch) {
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/* 
 *   return out
 * 
 * cpdef inline int c_rate2recs_2(int maxNN,int idx):             # <<<<<<<<<<<<<<
 *   cdef int out=idx%maxNN
 *   return out
 */

static PyObject *__pyx_pf_6kmc_cy_4c_rate2recs_2(CYTHON_UNUSED PyObject *__pyx_self, int __pyx_v_maxNN, int __pyx_v_idx) {
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As I am pretty new in the cython business, I would like to know how to get rid of most of the Python commands (cython -a flags this inline as pretty far away from pure C).

Answer 1

As I am pretty new in the cython business, I would like to know how to get rid of most of the python commands (cython -a flags this inline as pretty far away from pure C)

The trick is that if you can call your function nogil;

cpdef inline int c_rate2recs_2(int maxNN,int idx) nogil:
  cdef int out=idx%maxNN
  return out

then whatever yellow you see isn't actually generally going to Python. It could be an error-case, for example, or it could just be other types of mild checking. In the case of a cpdef, not only is a pure-C function made, a Python alias is made for calling from a Python scope. This will not affect speeds.

In this case some timings against a manually inlined loop showed no slowdowns, and removing inline did nothing, either, to the time. I imagine a case harder to optimise may show different characteristics, but the key is to profile.

Finally, speed-ups and removal of some of the error-checking can be had by using compiler directives.