Anurag Uniyal Anurag Uniyal - 4 months ago 29
Python Question

Change current process environment's LD_LIBRARY_PATH

Is it possible to change environment variables of current process?

More specifically in a python script I want to change

LD_LIBRARY_PATH
so that on import of a module 'x' which depends on some
xyz.so
,
xyz.so
is taken from my given path in LD_LIBRARY_PATH

is there any other way to dynamically change path from where library is loaded?

Edit: I think I need to mention that I have already tried thing like
os.environ["LD_LIBRARY_PATH"] = mypath
os.putenv('LD_LIBRARY_PATH', mypath)

but these modify the env. for spawned sub-process, not the current process, and module loading doesn't consider the new LD_LIBRARY_PATH

Edit2, so question is can we change environment or something so the library loader sees it and loads from there?

Answer

The reason

os.environ["LD_LIBRARY_PATH"] = ...

doesn't work is simple: this environment variable controls behavior of the dynamic loader (ld-linux.so.2 on Linux, ld.so.1 on Solaris), but the loader only looks at LD_LIBRARY_PATH once at process startup. Changing the value of LD_LIBRARY_PATH in the current process after that point has no effect (just as the answer to this question says).

You do have some options:

A. If you know that you are going to need xyz.so from /some/path, and control the execution of python script from the start, then simply set LD_LIBRARY_PATH to your liking (after checking that it is not already so set), and re-execute yourself. This is what Java does.

B. You can import /some/path/xyz.so via its absolute path before importing x.so. When you then import x.so, the loader will discover that it has already loaded xyz.so, and will use the already loaded module instead of searching for it again.

C. If you build x.so yourself, you can add -Wl,-rpath=/some/path to its link line, and then importing x.so will cause the loader to look for dependent modules in /some/path.

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