What are the differences between gdata.docs.service.DocsService and gdata.docs.client.DocsClient?

There're similarities (in authentication and a few other operations, e.g. both can get documents list), but what are the differences? Why do we need both of them?

I'm learning gdata api and i realized I can login using OAuth access token this way (using DocsClient):

self.client = gdata.docs.client.DocsClient()
self.client.auth_token = gdata.gauth.OAuthHmacToken(consumer.key, 
                                                    consumer.secret, 
                                                    user.access_token.key, 
                                                    user.access_token.secret, 
                                                  开发者_JS百科  gdata.gauth.ACCESS_TOKEN)

but I don't know how to do the same thing with DocsService.

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The file modification time within the source tree may provide some clues:

http://code.google.com/p/gdata-python-client/source/browse/#hg%2Fsrc%2Fgdata%2Fdocs

where service.py is 2 years old, so I suspect it is for an older API version, whereas the client.py works against DocumentsList API 3.0 currently. I believe DocsService is version 1 and now depreciated?