Far from a c expert but for me using ubuntu, the following works:

main.c:

#include "foo_api.h"
#include <stdio.h>


int main(int argc, char *argv[]) {
     Py_Initialize();
     initfoo();
     import_foo();
     double arr[5] = {1,2,3,4,5};
     int i = 0;
     foo(arr);
     for(i = 0; i < 5; i++)
    {
      printf("%f\n", arr[i]);
    }
     Py_Finalize();
     return 0;
}

foo.pyx:

cdef public api  foo(double* x):
   x[0] = 0.0

From the same directory:

$ cython foo.pyx 

Then:

$ cc -I/usr/include/python2.7 -I/usr/include/x86_64-linux-gnu/python2.7   -o foo  *.c -lpython2.7 

Then just run.

$ ./foo
0.000000
2.000000
3.000000
4.000000
5.000000

I used pkg-config --cflags python to get the flags:

 $ pkg-config --cflags python
-I/usr/include/python2.7 -I/usr/include/x86_64-linux-gnu/python2.7 

Without calling Py_Initialize (Initialize the Python interpreter. In an application embedding Python, this should be called before using any other Python/C API functions;), you will get:

Fatal Python error: PyThreadState_Get: no current thread
Aborted (core dumped)

Without initfoo() or import_foo() you get a:

 Segmentation fault (core dumped)

If you don't call Py_Finalize:

Py_Initialize a no-op when called for a second time (without calling Py_Finalize() first).

To get the delorean example from the docs to run:

main.py:

#include "delorean_api.h"
#include <stdio.h>
Vehicle car;


int main(int argc, char *argv[]) {
     Py_Initialize();
     initdelorean();
     import_delorean();
     car.speed = atoi(argv[1]);
     car.power = atof(argv[2]);
     activate(&car);
     Py_Finalize();
     return 0;
}

delorean.pyx:

ctypedef public struct Vehicle:
    int speed
    float power

cdef api void activate(Vehicle *v):
    if v.speed >= 88 and v.power >= 1.21:
        print "Time travel achieved"
    else:
        print("Sorry Marty")

The procedure is the same, the only change was I had to use ctypedef with the Vehicle struct or else in main or use I had t use struct Vehicle car; in main:

$ cython delorean.pyx
$ cc  -I/usr/include/python2.7 -I/usr/include/x86_64-linux-gnu/python2.7   -o delorean  *.c -lpython2.7  
$ ./delorean 1 1
Sorry Marty
$ ./delorean 100 2
Time travel achieved

You can also get it to work without using Py_Initialize etc...

In foo.pyx you just need to make the function public:

cdef public  foo(double* x):
   x[0] = 0.0

I added #include <python2.7/Python.h> just imported foo.hin main.c and removed Py_Initialize(); etc. Just importing python.h would not work for me but that may not be the case for everyone.

#include <python2.7/Python.h>
#include "foo.h"
#include <stdio.h>


int main(int argc, char *argv[]) {
     double arr[5] = {1,2,3,4,5};
     int i = 0;
     foo(arr);
     for(i = 0; i < 5; i++)
    {
      printf("%f\n", arr[i]);
    }

     return 0;
}

Compiling was the same:

$ cython foo.pyx 
$ cc -I/usr/include/python2.7 -I/usr/include/x86_64-linux-gnu/python2.7   -o foo  *.c -lpython2.7 
$ ./foo
0.000000
2.000000
3.000000
4.000000
5.000000

If you are using the api version then just include the api header or vice versa as per the docs However, note that you should include either modulename.h or modulename_api.h in a given C file, not both, otherwise you may get conflicting dual definitions.

To do the same with the delorean example I had to use libc.stdio to print the strings to avoid a segmentation fault:

from libc.stdio cimport printf

ctypedef public  struct Vehicle:
    int speed
    float power

cdef public void activate(Vehicle *v):
    if v.speed >= 88 and v.power >= 1.21:
        printf("Time travel achieved\n")
    else:
        printf("Sorry Marty\n")

main:

#include <python2.7/Python.h>
#include <stdio.h>
#include "delorean.h"

Vehicle car;


int main(int argc, char *argv[]) {
     car.speed = atoi(argv[1]);
     car.power = atof(argv[2]);
     activate(&car);
     return 0;
}

It might make more sense to return the values:

ctypedef public  struct Vehicle:
    int speed
    float power

cdef public  char* activate(Vehicle *v):
    if v.speed >= 88 and v.power >= 1.21:
        return  "Time travel achieved"
    return "Sorry Marty"

main:

#include <python2.7/Python.h>
#include <stdio.h>
#include "delorean.h"

Vehicle car;

int main(int argc, char *argv[]) {
     car.speed = atoi(argv[1]);
     car.power = atof(argv[2]);
     printf("%s\n",activate(&car));
     return 0;
}

1. Yes, at its core this is what Cython does. But ...
2. You don't need Cython, however, you do need libpython. You may feel like it doesn't use that many Python features, but I think if you try this you'll find it's not true -- you won't be able to separate your program from its dependence on libpython while still using the Python language.

Another option is PyPy, specifically it's translation toolchain, NOT the PyPy Python interpreter. It lets you translate RPython, a subset of the Python language, into C. If you really aren't using many Python language features or libraries, this may work.

PyPy is mostly known as an alternative Python implementation, but it is also a set of tools for compiling dynamic languages into various forms. This is what allows the PyPy implementation of Python, written in (R)Python, to be compiled to machine code.

If C++ is available, Nuitka is a Python to C++ compiler that works for regular Python, not just RPython (which is what shedskin and PyPy use).

when converting the code from python to c (using Cython) it converts it to c code which can be compiled into a shared object. in order to make it executable, you should add "--embed" to cython conversion command. this flag adds the 'main' function you need, so you could compile the c code into executable file. please notice you'll need the python .so runtime libraries in order to run the exec.

Check the documentation. It's not enough to do gcc x.c -o x.

This page explains compilation: http://docs.cython.org/src/reference/compilation.html

There's a lot more to it, but a direct answer is:

Compiling your .c files will vary depending on your operating system. Python documentation for writing extension modules should have some details for your system. Here we give an example on a Linux system:

$ gcc -shared -pthread -fPIC -fwrapv -O2 -Wall -fno-strict-aliasing -I/usr/include/python2.7 -o yourmod.so yourmod.c

Of course in your situation it's going to be something closer to -I/usr/include/python3.4, or even $(pkg-config --libs --cflags python3). And you're not building with -shared, because you want an executable.

Shortest "this has to work" set of commands is:

cython3 --embed greet.py -o greet.c
gcc $(pkg-config --libs --cflags python3) greet.c -o greet

You need to install pkg-config if it's missing.