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[Python-Dev] accumulator display syntax

Raymond Hettinger python at rcn.com
Tue Oct 21 14:58:55 EDT 2003 
[Skip Montanaro]
> I understand all that.  Still, the "best" syntax for these so-called
> iterator comprehensions might have been the current list comprehension
> syntax.  

Skip is right about returning to the basics.  Before considering 
some of the wild syntaxes that have been submitted, I suggest 
re-examining the very first proposal with brackets and yield.

At one time, I got a lot of feedback on this from comp.lang.python.  
Just about everyone found the brackets to be helpful and not misleading,
the immediate presence of "yield" was more than enough to signal that 
an iterator was being returned instead of a list:

	g = [yield (len(line),line)  for line in file  if len(line)>5]

This syntax is instantly learnable from existing knowledge about 
list comprehensions and generators.  The advantage of a near zero
learning curve should not be easily dismissed.

Also, this syntax makes is trivially easy to convert an existing
list comprehension into an iterator comprehension if needed to 
help the application scale-up or to improve performance.



Raymond Hettinger


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