Python Programming/Extending with ctypes

Extending with Pyrex Extending with Perl ctypes is a foreign function interface module for Python (included with Python 2.5 and above), which allows you to load in dynamic libraries and call C functions. This is not technically extending Python, but it serves one of the primary reasons for extending Python: to interface with external C code. Basics A library is loaded using the ctypes.CDLL function. After you load the library, the functions inside the library are already usable as regular Python calls. For example, if we wanted to forego the standard Python print statement and use the standard C library function, printf, you would use this: from ctypes import * libName = 'libc.so' # If you're on a UNIX-based system libName = 'msvcrt.dll' # If you're on Windows libc = CDLL(libName) libc.printf("Hello, World!\n") Of course, you must use the libName line that matches your operating system, and delete the other. If all goes well, you should see the infamous Hello World string at your console. Getting Return Values ctypes assumes, by default, that any given function's return type is a signed integer of native size. Sometimes you don't want the function to return anything, and other times, you want the function to return other types. Every ctypes function has an attribute called restype. When you assign a ctypes class to restype, it automatically casts the function's return value to that type. Common Types ctypes name C type Python type Notes None void None the None object c_bool C99 _Bool bool c_byte signed char int c_char signed char str length of one c_char_p char * str c_double double float c_float float float c_int signed int int c_long signed long long c_longlong signed long long long c_short signed short long c_ubyte unsigned char int c_uint unsigned int int c_ulong unsigned long long c_ulonglong unsigned long long long c_ushort unsigned short int c_void_p void * int c_wchar wchar_t unicode length of one c_wchar_p wchar_t * unicode Extending with Pyrex Extending with Perl