[Python-Dev] accumulator display syntax

[Sean Ross]

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(*[x*x 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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