[Python-3000] AST access (WAS: Adaptation vs. Generic Functions)

[Blake Winton]

Phillip J. Eby wrote:
> I tried doing something like this when I was writing RuleDispatch, and gave 
> up in disgust because there's no sane way to implement "and" and "or" 
> operations with this approach.  The bitwise operators (&, |, and ~) bind 
> too tightly to be used with comparison expressions, so doing something like 
> "x>y & z" would mean "x>(y&z)" instead of "(x>y)&z".

How would symbols, or ast access have helped you with that problem? 
Would you really go around manually mangling the parse tree to move the 
"&" higher in the branches somehow?

> So if you could backquote code to make an AST literal, you could spell 
> RuleDispatch overrides like:
>      @pprint_when(`isinstance(ob,list) and len(ob)<10`)
>      def pprint_short_list(ob):
>          ...
> And the database query use case could be done using something like:
>     db.query(`(row for row in some_table if row.x>42)`)"
> 
> Perhaps the backquote isn't the right character for this;

What do you think about the oft-maligned curly brace?

	@pprint_when({isinstance(ob,list) and len(ob)<10})
	def pprint_short_list(ob):
		db.query( {(row for row in some_table if row.x>42)} )
?  Not too heinous, in my view.
And it should be possible to tell the difference between it and a dict 
with a bit of a lookahead...  (Really it's the conflict with dict 
initialization that I expect to kill this proposal.)

Later,
Blake.