Set LD_LIBRARY_PATH before importing in python

Question

Python uses the PYTHONPATH environment-variable to determine in which folders it should look for modules. You can play around with it by modifying sys.path, which works nicely for pure Python-Modules. But when a module uses shared object files or static libraries, it looks for those in LD_LIBRARY_PATH (on linux), but this can't be changed as easily and is platform dependent as far as I know.

The quick-fix for this problem is of course to set the environment-variable or invoke the script like LD_LIBRARY_PATH=. ./script.py, but then you'll have to set it again for every new shell you open. Also, the .so files in my case will always be in the same directory as the .py file, but may very well be moved to another absolute path, so I'd like to set them automatically every time I invoke the script.

How can I edit the path in which the Python interpreter looks for libraries platform-independently on runtime?

EDIT:

I already tried os.environ['LD_LIBRARY_PATH'] = os.getcwd(), but to no avail.

Answer 1

UPDATE: see the EDIT below.

I would use:

import os  os.environ['LD_LIBRARY_PATH'] = os.getcwd()  # or whatever path you want 

This sets the LD_LIBRARY_PATH environment variable for the duration/lifetime of the execution of the current process only.

EDIT: it looks like this needs to be set before starting Python: Changing LD_LIBRARY_PATH at runtime for ctypes

So I'd suggest going with a wrapper .sh (or .py if you insist) script. Also, as @chepner pointed out, you might want to consider installing your .so files in a standard location (within the virtualenv).

See also Setting LD_LIBRARY_PATH from inside Python

Answer 2

My solution to this problem is to put this as the first line of a Python script (instead of the usual shebang):

exec env LD_LIBRARY_PATH=/some/path/to/lib /path/to/specific/python -x "$0" "$@" 

And here is how this works:

• with no shebang the current shell treats the file as a shell script,
• "exec" ensures that this first line is also the last command from this file executed by the shell,
• "env" is used here to set any environment variables, e.g. LD_LIBRARY_PATH,
• an exact path to Python's interpreter can specified or "env" can find one in PATH,
• "-x" is a Python's option which causes the first line to be ignored by the Python interpreter,
• "$0" is the script name, "$@" is substituted by positional parameters.