[Python-Dev] accumulator display syntax (original) (raw)

Sean Ross seandavidross at hotmail.com
Fri Oct 17 12:43:31 EDT 2003

Hi. I've not posted to this group before, but I've been following most of the discussions on it with interest for about 6 months. Yesterday I saw this post:

Guido van Rossum wrote:

I don't have a proposal for generator comprehension syntax though, and [yield ...] has the same problem.

I actually like the [yield ...] syntax, (I find the intent clear, and have no expectations of its returning a list) but since that doesn't look like it will be happening, I've tried to think of some other possible syntax. I've come up with 16 different possibilities so far, including [yield ...], which I've listed below. I'm not advocating any one of them (in fact, many of them are abhorrent), I'm just listing some possibilities, in no particular order other than as they occurred to me:

(1) no delimiter

sumofsquares = sum(yield x*x for x in myList)

(2) brackets

sumofsquares = sum([yield x*x for x in myList])

(3) parentheses

sumofsquares = sum((yield x*x for x in myList))

(4) braces

sumofsquares = sum({yield x*x for x in myList})

(5) pipes

sumofsquares = sum(|yield x*x for x in myList|)

(6) slashes

sumofsquares = sum(/yield x*x for x in myList/)

(7) carets

sumofsquares = sum(^yield x*x for x in myList^)

(8) angle brackets

sumofsquares = sum(<yield x*x for x in myList>)

(9) sigil @

sumofsquares = sum(@yield x*x for x in myList@)

(10) sigil $

sumofsquares = sum($yield x*x for x in myList$)

(11) question marks

sumofsquares = sum(?yield x*x for x in myList?)

(12) ellipses

sumofsquares = sum(...yield x*x for x in myList...)

(13) yield:

sumofsquares = sum(yield:[x*x for x in myList])

(14) unpacking (*)

sumofsquares = sum([xx for x in myList])

(15) <-

sumofsquares = sum(<-[x*x for x in myList])

#(16) ^ sumofsquares = sum(^[x*x for x in myList])

These last few suggestion (from (13) on) may require some explanation. The notion I've had for "yield:" is to have it act something like a lambda so that the list comprehension is not evaluated, i.e., no list is constructed in memory. Instead, an iterator is created that can be used to generate the items, one at a time, that would have been in that list. Something like

def squares(myList): for x in myList: yield x*x

sumofsquares = sum(squares(myList))

The other suggestions, after (13), are based on this same notion.

Okay. So, there are some generator comprehension syntax ideas. Hopefully they will be useful, even if they just serve as items to point to and say "we definitely don't want this".

I thank you for your time, and I apologize if these unsolicited suggestions are unwanted.

Sean Ross

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