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[Python-Dev] accumulator display syntax

Alex Martelli aleaxit at yahoo.com
Fri Oct 17 16:01:50 EDT 2003 
On Friday 17 October 2003 08:57 pm, Skip Montanaro wrote:
   ...
> Forgive my extreme density on this matter, but I don't understand what
>
>     (yield x for x in S)
>
> is supposed to do.  Is it supposed to return a generator function which I
> can assign to a variable (or pass to the builtin function sum() as in your
> example) and call later, or is it supposed to turn the current function
> into a generator function (so that each executed yield statement returns a
> value to the caller of the current function)?

Neither: it returns an iterator, _equivalent_ to the one that would be
returned by _calling_ a generator such as

def xxx():
    for x in S:
        yield x

like xxx() [the result of the CALL to xxx, as opposed to xxx itself], (yield: 
x for x in S) is not callable; rather, it's loopable-on.

> you don't like lambda, I can't quite see why syntax this is all that
> appealing.

I don't really like the current state of lambda (and it will likely never get 
any better), I particularly don't like the use of the letter lambda for this 
idea (Church's work notwithstanding, even Paul Graham in his new lispoid 
language has chosen a more sensible keyword, 'func' I believe), but I like 
comprehensions AND iterators, and the use of the word yield in generators.
I'm not quite sure what parallels you see between the two cases.


Alex
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