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Path-independent management of shared C libraries within the Python package

Let's say I have a Foo package organized like this:

Foo\
    __init__.py
    foo.py
    bar.py
    lib\
        libwhatever.so

My foo.py module uses python types to wrap the C methods contained in my libwhatever.lib, which includes checking lib where it should be. 2 questions:

1) How to check in my package that the required lib is in its place (in Foo \ lib), wherever the entire Foo package is placed?

Right now, the path to my lib is hard-coded, but since I can distribute things later, the problem will come.

2) Then I have a module bar.py that contains a slower version of C-routines in Python inside libwhatever. I would like to use them instead of whether the libwhatever import fails. Is there a way to abstractly switch between versions of C and Python routines to succeed or fail to import a library?

Thank you in advance for your advice.

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1 answer

Assuming you are working on Linux, I think you will either have to add this .so file to the library search path, or add the module directory to your path. Take a look at ldconfig. man ldconfig. Once you do this, you can use ctypes.util.find_library(). Otherwise, you will need the full path to the .so file to use cdll().

, , , - - :

from ctypes import CDLL
import Foo
try:
    MyLib = CDLL(Foo.__path__[0] + '/lib/libwhatever.so')
except OSError:
    from Foo import bar as MyLib

, , ...

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