Exploring ctypes (2)

I used an example from before (here) to make a dylib and then called the functions using ctypes. It seems very easy:

add1.c

int f1(int x) { return x + 1; }

add2.c

int f2(int x) { return x + 2; }

> gcc -g -Wall -c add*.c > gcc -dynamiclib -current_version 1.0 add*.o -o libadd.dylib > file libadd.dylib libadd.dylib: Mach-O 64-bit dynamically linked shared library x86_64

> python Python 2.7.1 (r271:86832, Jun 16 2011, 16:59:05) [GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import ctypes >>> pre = '/Users/telliott/Desktop' >>> libadd = ctypes.CDLL(pre + '/libadd.dylib', ctypes.RTLD_GLOBAL) >>> x = libadd.f1(1) >>> x 2 >>> y = libadd.f2(x) >>> y 4 >>>

I guess one question is how to alter / determine the search path for ctypes in loading libraries. libc is in /usr/lib, but libpng is in /usr/X11/lib, as we discussed the other day (here):

>>> libc = ctypes.CDLL('libc.dylib', ctypes.RTLD_GLOBAL) >>> libpng = ctypes.CDLL('libpng.dylib', ctypes.RTLD_GLOBAL) Traceback (most recent call last): File "", line 1, in File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ctypes/__init__.py", line 353, in __init__ self._handle = _dlopen(self._name, mode) OSError: dlopen(libpng.dylib, 10): image not found >>> pre = '/usr/X11/lib/' >>> libpng = ctypes.CDLL(pre + 'libpng.dylib', ctypes.RTLD_GLOBAL) >>>

>>> import ctypes.util >>> ctypes.util.find_library('libpng.dylib') >>> ctypes.util.find_library('png') >>> ctypes.util.find_library('AGL') '/System/Library/Frameworks/AGL.framework/AGL'

Obviously, find_library doesn't search /usr/X11/lib. Wonder if there is a way to tell it what we want?

After we look at Andrew's more sophisticated examples, we'll try something relevant to bioinformatics