Download Python and C

Python
Python and other languages
Marcin Młotkowski
22nd May, 2013
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
1
Extending Python by C programs— Python/C API
2
Embedding Python in C
3
Other Python platforms
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Challenges of joining two languages
Topics
different data typed (lists, collections, strings);
passing and returning values;
new values creation;
exception handling;
memory management.
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
How to add a new function to Python
Exercise
A module with function computing the average value of elements of
a list.
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
How to add a new function to Python
Exercise
A module with function computing the average value of elements of
a list.
Elements of implementation:
a header file <Python.h>;
a function implementation;
a mapping of C function into "Python name";
an initializing function of the name initmodule_name.
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
A function implementation
extern PyObject * mean(PyObject *, PyObject *);
PyObject * mean(PyObject * self, PyObject * args)
{
int suma = 0, n, i;
PyObject * res;
PyObject * item;
PyObject * lista;
lista = PySequence_ITEM(args, 0);
if (!PyList_Check(lista)) printf("This is not a list!\n");
n = PyList_Size(lista);
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Implementation, cont.
the function, cont.
for (i = 0; i < n; i++) {
item = PyList_GetItem(lista, i);
if (!PyInt_Check(item)) continue;
suma += PyInt_AsLong(item);
}
res = Py_BuildValue("i", suma/n);
Py_INCREF(res);
return res;
}
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Wrapping the function
#include <python2.4/Python.h>
extern PyObject * mean(PyObject *, PyObject *);
PyObject * mean(PyObject * self, PyObject * args)
{ ... }
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Wrapping the function
#include <python2.4/Python.h>
extern PyObject * mean(PyObject *, PyObject *);
PyObject * mean(PyObject * self, PyObject * args)
{ ... }
static PyMethodDef modulik[ ] = {
{ "mean", mean, METH_VARARGS, "First function"},
{ NULL, NULL, 0, NULL }
};
PyMODINIT_FUNC
initmodulik(void) {
Py_InitModule("modulik", modulik);
}
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Compilation and installation
setup.py
from distutils.core import setup, Extension
module1 = Extension(’modulik’, sources = [’test.c’])
setup(name = ’MyPackage’,
version = ’1.0’,
description = ’Demonstration package’,
ext_modules = [module1])
Compilation and installation
$ python setup.py build
$ python setup.py install
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Data types in Python
Everything in Python is an object.
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
New values
Creation new values
PyObject* PyInt_FromLong(long ival)
PyObject* Py_False
PyObject* Py_True
PyObject* PyList_New(Py_ssize_t len)
PyObject* PyString_FromString(const char *v)
PyObject *Py_BuildValue(char *format, ...);
Py_BuildValue()
Py_BuildValue("ss", "hello", "world")
Py_BuildValue("[i,i]", 123, 456)
Py_BuildValue("{s:i,s:i}",
"abc", 123, "def", 456)
Marcin Młotkowski
Python
None
(’hello’, ’world’)
[123, 456]
{’abc’: 123, ’def’: 456}
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Lists
Accessing lists
PyObject* PyList_GetItem(PyObject *list, Py_ssize_t index)
int PyList_SetItem(PyObject *list, Py_ssize_t index, PyObject *item)
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Objects
Accessing object fields
PyObject* PyObject_GetItem(PyObject *o, PyObject *key)
int PyObject_SetItem(PyObject *o, PyObject *key, PyObject *v)
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Standard multiarguments functions
A header of the function
PyObject * foo(PyObject * self, PyObject * args)
Argument parsing
int PyArg_ParseTuple(PyObject *args, const char *format, ...)
Register the function in a function table
{ "mean", mean, METH_VARARGS, "First function"},
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Memory management
Memory management strategy
Each object has a counter of references.
If the counter is equal to zero, the object is removed.
C programs must take care of objects’ counters.
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Counters
Incrementing counter
void Py_INCREF(PyObject *o)
Decrementing counter
void Py_DECREF(PyObject *o)
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Counters
Incrementing counter
void Py_INCREF(PyObject *o)
Decrementing counter
void Py_DECREF(PyObject *o)
Remainder
res = Py_BuildValue("i", suma/n);
Py_INCREF(res);
return res;
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Make our life easier
Boost library:
+ joining Python with C++
+ easier than C API
- sometimes it is impossible to avoid C API, but there
is promise...
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
How to execute Python programs
Py_Initialize();
PyRun_SimpleString("i = 2");
PyRun_SimpleString("i = i*i\nprint i");
Py_Finalize();
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Execution of programs in file
Py_Initialize();
FILE * f = fopen("test.py", "r");
PyRun_SimpleFile(f, "test.py");
Py_Finalize();
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Compilation
gcc -lpython2.4 test.c
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Direct Python functions invocation
Variable declarations
PyObject *pName, *pModule, *pArgs, *pFunc, *pValue;
Importing a Python module
Py_Initialize();
pName = PyString_FromString("modulik");
pModule = PyImport_Import(pName);
Drag a function form module
pFunc = PyObject_GetAttrString(pModule, "foo");
Function invocation
pValue = PyObject_CallObject(pFunc, pArgs);
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Jython
Features of Jython
implementation on Java Virtual Machine;
compiles to .class files;
access to Java library;
full compatibility with standard implementation (the same
regression tests).
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
IronPython
Implementation for Mono framework;
partially compatible with Python 2.4
Marcin Młotkowski
Python
Extending Python by C programs— Python/C API
Embedding Python in C
Other Python platforms
Python for S60
Nokia implementation for mobile phones with Symbian 60
implements Python 2.2.2;
access to hardware (SMS’s, power of signal, video recording,
calling and receiving connections);
support for GPRS and Bluetooth;
access to 2D API and OpenGL.
Marcin Młotkowski
Python