Use find_library to load libopenslide-0.dll for Windows

[SachidanandAlle]

Currently user has to copy libopenslide-0.dll into system folder. If user has downloaded the openslide zip and added the openslide/bin to PATH, it fails to load libopenslide-0.dll.
Hence better to use find_library to find and load the dll file for windows as well.

[bgilbert]

On Python 3.8 and above, use this code to specify the directory containing libopenslide-0.dll:

import os
with os.add_dll_directory(r'c:\path\to\openslide\directory'):
    import openslide

For more info, see #115 and #150.

[SachidanandAlle]

so user can not use PIP package directly on windows.. like me, others have to add/modify something more to continue.. i mean user have to write extra lines on top to handle this error...

i am fine with any solution that makes usage little simplified without doing any top-up code to use OpenSlide Python on windows. specially not comfortable of using/hardcoding the dir path for openslide inside python code..

[bgilbert]

You should still be able to use pip to install OpenSlide Python. You just need an additional line before the import statement. This isn't unique to OpenSlide Python; it's a Python policy change in ≥ 3.8 to tighten the security rules for loading DLLs.

You don't need to hardcode the path if you don't want to. You can read the path from an environment variable or a config file, or use a path calculated from the path of your Python module.

[j-sieger]

On Python 3.8 and above, use this code to specify the directory containing libopenslide-0.dll:

import os
with os.add_dll_directory(r'c:\path\to\openslide\directory'):
    import openslide

For more info, see #115 and #150.

@SachidanandAlle
I am facing the same issue on Amazon linux2(EC2) while starting the MONAILalbel App. I need 'libopenslide.so.0' file. I am not able find .so file in my system path to add the path like you edited the lowlevel.py file.

Can you please help me here.

[j-sieger]

On Python 3.8 and above, use this code to specify the directory containing libopenslide-0.dll:

import os
with os.add_dll_directory(r'c:\path\to\openslide\directory'):
    import openslide

For more info, see #115 and #150.

@bgilbert :
What is the path here to find libopenslide.so.0 file. I could not find any .so file in the system paths. I was able find .dll from here (https://openslide.org/download/) but no so files here as well.

[bgilbert]

@j-sieger OpenSlide Python requires OpenSlide. If it's not packaged in your distribution, you'll need to install from source.