If the underlying libraries are not installed, importing the openslide or pyvips modules fails. This PR replaces the module with a mock module that raises an exception only when the module is actually used.
Looks good, thanks! I will refactor this a little as otherwise the errors will get swallowed by the file import errors, I think they should be more explicit.
An attempt to fix #20
If the underlying libraries are not installed, importing the openslide or pyvips modules fails. This PR replaces the module with a mock module that raises an exception only when the module is actually used.