I searched the web for an existing and supported SOAP library for Python 3. (both client and server)
Here the list of libraries I've found:
Python 2:
Python 3:
Does this list seems complete to you? (FYI, I used this post as starting point (The purpose of that post was the same but for Python 2))
ladon seems to me the only existing framework for Python 3 but can AFAIK only be used for implementing the server side.
NO: I don't want to migrate one of the discontinued Python 2 projects myself. I am looking for a supported project with an active team providing help if needed.
Updated on 28/09/2013
Depending on the complexity of the service, you could use ladon for the server side and mock up the client by hand until there's a better solution available.
Just call the service with suds (or similar) with logging turned on and note the SOAP wrapping on the request. Use that to wrap your request and call the service with plain http.
It's not an ideal solution, but it can get you by until you have a package to replace it.