Embedding the Python interpreter

Jason Furtney

@jkfurtney

Rock Mechanics

Rock Mechanics

Rock Mechanics

Rock Mechanics

Numerical Modeling

Numerical Modeling

Ask the experts

Python

My C

extension

code

Extension module

My C program

Embedding and extending

Python

My C

extension

code

 def say_hello(name):
     "Greet somebody."
     print "Hello %s!" % name

#include <Python.h>

static PyObject*
say_hello(PyObject* self, PyObject* args)
{
    const char* name;

    if (!PyArg_ParseTuple(args, "s", &name))
        return NULL;

    printf("Hello %s!\n", name);

    Py_RETURN_NONE;
}

static PyMethodDef HelloMethods[] =
{
     {"say_hello", say_hello, METH_VARARGS, "Greet somebody."},
     {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC
inithello(void)
{
     (void) Py_InitModule("hello", HelloMethods);
}

Basic extending

Automatic generation of wrapper code

• SWIG
• XDress
• Cython
• cffi
• Boost::Python

​​

We rolled our own...

#include <Python.h>

int main(int argc, char *argv[])
{
    /* Pass argv[0] to the Python interpreter */
    Py_SetProgramName(argv[0]);

    /* Initialize the Python interpreter.  Required. */
    Py_Initialize();

    /* Add a static module */
    inithello();

    ...

Basic embedding

Call Python functions from C

Call C functions from Python

Not in the documentation

Redefine the sys.stdin and sys.stdout objects

Write a Python function to compile code, execute code, capture output and handle errors.

Write as much as possible in Python and call it from C.

Pitfalls

Reference counting is hard

Object life-cycle issues

Threading and GUI updates

Compiler compatibility

Python state cannot be serialized

Victories

IPython Qt console 

Qt integration via PySide

NumPy, SciPy and Matplotlib integration

Our customers can use any 3rd party Python library 

End product