While functionally they are the same, the session/resource stuff is not safe to use across multiple threads and subprocesses, and the client stuff is. The former is a bit easier to use directly than the latter, but this does not impact the user, because smart_open is doing all the work.

I also refactored the way we pass keyword parameters to boto3. Previously, we had a separate parameter for each boto3 function. This was a pain, because this made parameter lists longer for each new function, e.g.

• resource_kwargs
• multipart_upload_kwargs
• singlepart_upload_kwargs
• object_kwargs

This PR moves all of the above parameters into a single nested dict and introduces a wrapper that transparently injects the parameters into the required function call.

This does break backwards compatibility, so will need a major version bump when releasing.