Updated 02 and 03 patches (mostly) in line with Antoine's review comments:

> 2) poplib_02_server_capabilities_v3.diff:
> - please try to follow PEP 8 (i.e. `capa = {}` not `capa={}`)
> - I think the capa() result should be a dict mapping str keys to str > values (not bytes), since that part of the POP3 protocol seems to
> have a well-defined character set (ASCII)

Completely right. Done.

> 3) poplib_03_starttls_v3.diff:
>
> - same comment about PEP 8

where?

> - why did you change the signature of the _create_socket() 
>  method? it looks gratuitous

undone

> - the new method should be called starttls() as in other modules, not >  stls()

Here I'm following: at :ref:`pop3-objects` in Doc/library/poplib.rst, 

  All POP3 commands are represented by methods of the same name, in
  lower-case; most return the response text sent by the server.

IMHO, having a single method with a name different than the underlying
POP command would just be confusing. For this reason, I'd rather avoid
adding an alias like in

    starttls = stls

or the reverse...

> - starttls() should only take a context argument; no need to support > separate keyfile and certfile arguments

Right, non need to mimick pre-SSLContext method signatures!

> - what is the point of catching errors like this:
> [...]

undone