How use correctly a .dll file in python on linux and mac

Question

I have been trying to use a dll library from CNES in python. My first approach was trough ctypes and i did something like:

from ctypes import *
cdll.LoadLibrary("dll/propa64.dll")

This simple loading goes very smooth on windows but i have trouble on mac/linux. More specifically when i try to run the code on MacOS i get:

---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-6-74c6935de494> in <module>
----> 1 cdll.LoadLibrary("dll/propa64.dll")

~/opt/anaconda3/lib/python3.7/ctypes/__init__.py in LoadLibrary(self, name)
    440
    441     def LoadLibrary(self, name):
--> 442         return self._dlltype(name)
    443
    444 cdll = LibraryLoader(CDLL)

~/opt/anaconda3/lib/python3.7/ctypes/__init__.py in __init__(self, name, mode, handle, use_errno, use_last_error)
    362
    363         if handle is None:
--> 364             self._handle = _dlopen(self._name, mode)
    365         else:
    366             self._handle = handle

OSError: dlopen(dll/propa64.dll, 6): no suitable image found.  Did find:
    dll/propa64.dll: unknown file type, first eight bytes: 0x4D 0x5A 0x90 0x00 0x03 0x00 0x00 0x00
    /range/code_python/propa/dll/propa64.dll: unknown file type, first eight bytes: 0x4D 0x5A 0x90 0x00 0x03 0x00 0x00 0x00

and in Linux(to be precise is a linux docker image on a macos host) i get:

---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
<ipython-input-3-74c6935de494> in <module>
----> 1 cdll.LoadLibrary("dll/propa64.dll")

/opt/conda/lib/python3.7/ctypes/__init__.py in LoadLibrary(self, name)
    440 
    441     def LoadLibrary(self, name):
--> 442         return self._dlltype(name)
    443 
    444 cdll = LibraryLoader(CDLL)

/opt/conda/lib/python3.7/ctypes/__init__.py in __init__(self, name, mode, handle, use_errno, use_last_error)
    362 
    363         if handle is None:
--> 364             self._handle = _dlopen(self._name, mode)
    365         else:
    366             self._handle = handle

OSError: dll/propa64.dll: invalid ELF header

Now it is preatty clear that there is some sort of incompatibility on Linux and Macos for this dll. My question are:

why is that?
is there a way to make this library more "compatible" ?

I have been looking around a bit and maybe Cython could be useful but i'm not entirely sure. Thank in advance for the help!

Someone pointed out this: Importing a dll in python on Ubuntu but even though this could be a valid workaround i would rather prefer to solve the problem at is core.

Does this answer your question? [Importing a dll in python on Ubuntu](https://stackoverflow.com/questions/7876225/importing-a-dll-in-python-on-ubuntu) — chrisbyte, Jul 10 '20 at 14:44
Well somehow yes but i would prefer to solve the problem at the root and get some less cumbersome stuffs — Paolo Squadrito, Jul 10 '20 at 14:50
Did you contact CNES about that library? They could help you.... — Basile Starynkevitch, Jul 10 '20 at 15:04
When the C code is compiled, it can only be executed on the platform it was compiled on. So a DLL library (compiled for Windows) is useless on Linux/MacOS, and vice versa. If you want to use the library on Linux, you need to download `propa64.so` and load it instead of the DLL file. On MacOS, you'd need a `propa64.dylib`, but it seems that the developer doesn't offer it, so your only possibility is to obtain the source code and compile it on MacOS yourself. — hoefling, Jul 10 '20 at 17:07
@hoefling thanks that was very helpful. I will try to contact the developer for the source code like also Basile Starynkevitch suggested. But for now windows and linux will be sufficent — Paolo Squadrito, Jul 10 '20 at 17:26

score 0 · Accepted Answer · answered Jul 11 '20 at 16:43

0

As hoefling explained, *.dll libraries are only for Windows. At the site you've specified, there already are libraries built for and Linux.

The static lib propa64.a definitely should work on Linux, and I guess if it's for x86 64-bit platform, it should also work on MacOS.

answered Jul 11 '20 at 16:43

olha

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Both .a and .so works for linux (in my case a docker container on a mac host) unfortunately it does not with mac but for now windows and linux will do just fine. Thank you all for your help! – Paolo Squadrito Jul 11 '20 at 17:14

How use correctly a .dll file in python on linux and mac

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