Changing LD_LIBRARY_PATH at runtime for ctypes

Question

How do you update this environment variable at runtime so that ctypes can load a library wherever? I've tried the following and neither seem to work.

from ctypes import *
os.environ['LD_LIBRARY_PATH'] = "/home/starlon/Projects/pyCFA635/lib"  
os.putenv('LD_LIBRARY_PATH', "/home/starlon/Projects/pyCFA635/lib")  
lib = CDLL("libevaluator.so")

Answer 1

By the time a program such as Python is running, the dynamic loader (ld.so.1 or something similar) has already read LD_LIBRARY_PATH and won't notice any changes thereafter. So, unless the Python software itself evaluates LD_LIBRARY_PATH and uses it to build the possible path name of the library for dlopen() or an equivalent function to use, setting the variable in the script will have no effect.

Given that you say it doesn't work, it seems plausible to suppose that Python does not build and try all the possible library names; it probably relies on LD_LIBRARY_PATH alone.

Answer 2

CDLL can be passed a fully qualified path name, so for example I am using the following in one of my scripts where the .so is in the same directory as the python script.

import os
path = os.path.dirname(os.path.realpath(__file__))
dll = CDLL("%s/iface.so"%path)

In your case the following should suffice.

from ctypes import *
lib = CDLL("/home/starlon/Projects/pyCFA635/lib/libevaluator.so")