[Email-SIG] Plans for email 6.0

[Barry Warsaw]

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Hello everyone.

Today's the last day of Pycon 2009 sprints and I'm eager to return  
home and see my family.  Chris Withers and I had a good day sprinting  
on the email package before he had to jet out, and although we only  
closed one bug in Python 2.7 (this is where Chris's mantra "backport,  
backport" begins :) we had a lot of good discussions about how and  
where to fix outstanding problems in email.

I have lots of ideas on how to improve the email package.  I plan on  
creating a bit of space on the Python wiki to consolidate my thoughts  
and to coordinate implementation.  I'm hoping some of you will be  
interested enough to help with design, testing, use cases, and coding.

We have a few older pages in the wiki covering the email package:

http://wiki.python.org/moin/EmailSigSprint
http://wiki.python.org/moin/EmailSprint

Some of this we've accomplished.  Here's a rambling of some of my  
thoughts on things we should do.

* Turn all header values into Header instances.  It's difficult and  
error prone to have to manage both strings and Headers as values, so  
they should always be Header instances.  We should add a registry of  
Header subclasses, based on the lower cased header name, for allowing  
higher level semantic folding of header strings.

* Implement a Message subclass registry for parsing.  This would allow  
the parser to create custom subclasses based on the Content-Type found  
while parsing the message.

* Bytes and string interfaces.  This is the trickiest one.  I think  
that internally, header names and values, and payloads should all be  
represented as bytes.  But APIs should accept bytes and strings,  
converting to bytes on input, and provide APIs to extract information  
as either bytes or strings.  I've thought about a few ways to do this  
cleanly, but haven't found anything I particularly like yet.  Remember  
that in email in Py2 is horribly broken in its discrimination between  
bytes and strings, but Py3 forces us to make a choice (which is a good  
thing).

* Clean up the API.  Where possible, simple attribute access should be  
the norm.  Let's get rid of dumb API decisions (like str(msg)  
including the Unix-From).  Let's fix the whole  
get_payload(decode=True) debacle.  Let's fix stuff like needing to  
specify unicode encodings twice in the same call.  Etc.

* Add an external storage API so that messages with huge binary  
payloads don't need to be fully stored in memory.

* Let's target Python 3.1 (coming very soon) if possible, or Python  
3.2 if not.  We should back port email 6.0 to Python 2.x, though we'll  
have to decide how far back we should go (my suggestion: no earlier  
than Python 2.5).

* Fix the myriad of bugs in the tracker!

That's it for now.  I'll figure out a place in the wiki for this and  
we can start capturing our thoughts there.  One thing I've heard  
pretty consistently is that while the email package has its problems,  
it's one of the best email packages available for any language.  Let's  
make it rock.

Barry

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