Changing LD_LIBRARY_PATH at runtime for ctypes

user_104304 0
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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")
ctypes python
5 Answers

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.

user_151680

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")
user_104710

Setting LD_LIBRARY_PATH to the path where libraries are placed won't work here and ctypes will not notice any changes. So, you need to set this at the source and run ldconfig before your script to take this into account. Moreover setting the os environment or any PATH variable in the script will have no effect.

I was facing a similar issue and spent around a day to figure this out.

mkdir -p /etc/ld.so.conf.d/
echo "/home/starlon/Projects/pyCFA635/lib" > /etc/ld.so.conf.d/mycustomPath.conf

ldconfig

Then verify if the path is set with:

ldconfig -v | less

After this is done, try to run your script. This has worked for me and should work for you also.

You can see below URL which helped me to resolve this:

https://www.cyberciti.biz/faq/linux-setting-changing-library-path/

Note: I realized the question is old, however I wanted to contribute to this as the accepted answer alone was not actually solving my problem.

user_33276850
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