[Email-SIG] fixing the current email module

[Barry Warsaw]

On Oct 9, 2009, at 2:26 AM, Glenn Linderman wrote:

> Then the Postel principle is un-Pythonic, and to be Pythonic any  
> incorrect email should produce an error, and be unreadable. Again, I  
> mentioned producing a defect report.  That is not passing an error  
> silently.

There's no conflict between principles here if you keep clear in your  
mind the two different patterns we're talking about.  When parsing raw  
data, we soldier on in the face of errors as best we can, never  
raising exceptions, but recording defects.  When manipulating the  
model, we throw exceptions as early as possible because these are  
application errors and the client controls the application.

> The un-Pythonic thing is returning defect reports instead of raising  
> errors.  There is no way for a simple assignment interface to return  
> an error, because the API for simple assignment doesn't have an in- 
> band signaling mechanism.

This "assignment interface" falls under "manipulating the model".  It  
does reveal an important point though: the parser may not be able to  
use the same API that model manipulation uses.  It may need to use a  
lower-level (read: more permissive) interface to the model.  The  
current parser mostly works well though because the current model  
doesn't do any standards checking.  Wanna create a 10k Subject  
header?  Fine!  In practice this works well, so perhaps we need to  
think about how "RFC enforcement" can be overlaid on the model.

-Barry

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