What methods can I use to return a struct to a Python Ctypes call to the function in a shared object? -

i have following c file compiling shared object. load .so shared object via ctypes in python. can call function ctypes, , function prints correct temp , humidity, can't seem struct main code. how can struct c function , how can retrieve fields within python.

#!/bin/python  ctypes import * class hmtemp(structure):  _fields_ = [ ("temp", c_double) , ("humidity", c_double) ] dhtlib = 'libdht4py.so' hlibc = cdll(dhtlib) hmtemp = hlibc.readdht() print hmtemp.temp 

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#define bcm2708_peri_base        0x20000000 #define gpio_base                (bcm2708_peri_base + 0x200000) /* gpio controller */  #include <stdio.h> #include <string.h> #include <stdlib.h> #include <dirent.h> #include <fcntl.h> #include <assert.h> #include <unistd.h> #include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/time.h> #include <bcm2835.h> #include <unistd.h>  #define maxtimings 100  struct dhstruct {      double temp;  double humidity; }  ;   struct dhstruct readdht();   int bits[250], data[100]; int bitidx = 0;  struct dhstruct readdht() {   bcm2835_init() ;    int type = 11 ;    int pin = 4 ;   struct dhstruct dhts;   int counter = 0;   int laststate = high;   int j=0;    // set gpio pin output   bcm2835_gpio_fsel(pin, bcm2835_gpio_fsel_outp);    bcm2835_gpio_write(pin, high);   usleep(500000);  // 500 ms   bcm2835_gpio_write(pin, low);   usleep(20000);    bcm2835_gpio_fsel(pin, bcm2835_gpio_fsel_inpt);    data[0] = data[1] = data[2] = data[3] = data[4] = 0;    // wait pin drop?   while (bcm2835_gpio_lev(pin) == 1) {     usleep(1);   } //while    // read data!   (int i=0; i< maxtimings; i++) {     counter = 0;     while ( bcm2835_gpio_lev(pin) == laststate) {     counter++;     //nanosleep(1);     // overclocking might change this?         if (counter == 1000)       break;     }//while     laststate = bcm2835_gpio_lev(pin);     if (counter == 1000) break;     bits[bitidx++] = counter;      if ((i>3) && (i%2 == 0)) {       // shove each bit storage bytes       data[j/8] <<= 1;       if (counter > 200)         data[j/8] |= 1;       j++;     }//if   } //for      dhts.temp = data[2] ;     dhts.humidity = data[0] ;      printf("temp = %5.2f *c, hum = %5.2f \%\n", dhts.temp , dhts.humidity );    return dhts; }//function 

to combine c/c++ , python recommend use cython. cython able pass objects (eg. numpy arrays) c/c++, fill data , python-code.

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here minmal example:

the c-skript: (c_example.c)

#include <stdlib.h> #include <math.h>  void c_claculate(double *x, int n) {   int i;   (i = 0; i<n;i++) {     x[i]+=i*i;   } } 

the python-skript: (example.py)

from numpy import * example import *  data=zeros(10) calculate(data) print data 

the .pyx file: (example.pyx)

import cython import numpy cimport numpy  # declare interface c code cdef extern void c_claculate(double *x, int n)  # cython interface c function def calculate(numpy.ndarray[double, ndim=1, mode='c'] x not none):     cdef int n = x.shape[0]     c_claculate(&x[0],n)     return x 

and setup file: (setup.py)

from distutils.core import setup distutils.extension import extension cython.distutils import build_ext import numpy  setup(     cmdclass = {'build_ext': build_ext},     ext_modules = [         extension("example",                   sources=["example.pyx", "c_example.c"],                   include_dirs=[numpy.get_include()]                   )     ], ) 

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now can compile skript running

python setup.py build_ext -fi 

and execute python skript.

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cython should available via pip on pi.