Re: Append behavior of __setitem__

At 16:43 +0900 04/11/2009, Stephen J. Turnbull wrote:
>Barry Warsaw writes:
>
> > So I'm just starting to read RFC 5322 and I'm starting by skimming
> > over Appendix A (differences between RFC 5322 and 2822).
>
>I know Barry's a big supporter of the Postel Principle.  As a
>guideline[1], how far back should we be lenient?  RFC 822 (no leading "2"
>;-)?

Sure.  The header field should be parsed, if possible, and possibly add a
defect to the message.  For some header fields, the data should be added to
the previous Header instance; for others, an extra Header instance might
need to be created.

Message /generation/ should comply with what was in RFC 2822, where this
requirement was added, and also the new RFC 5322.


>Footnotes:
>[1]  Presumably over time we'll accrete definitely non-conforming
>practices that we need to accept and do something sane with (eg, we
>can't just raise ArmageddonException because we get a header with
>8-bit characters in it).  But I think we also should have a plan for
>formerly acceptable syntax that has been restricted in more recent
>RFCs, etc.

Any email parser must cope with both obsolete-* syntax and common bad
practices.  Python's already does in various places.
-- 
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