Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
Martin v. Löwis wrote: That's not the full syntax. The full syntax is [ test for exprlist in testlist list-iter-opt ] where test can be an arbitrary expression: and, or, lambda, +, -, ... exprlist can be a list of expression, except for boolean and relational expressions (but I think this is further constrained semantically) testlist list a list of tests list-iter-opt is optional, and can be another for or if block Aren't these names a bit mixed up w.r.t. what's in that position? As far as I know test is not a test but a function as it produces any value not just True/False exprlst is a list of names, not arbitrary expressions testlist is anything which will produce an iterator Or so I've understood so far. So a more complex example is [ lambda a: a[x]+y*z for x,y in A for z in B if x z] I'm schocked ;-) --eric ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
Eric Nieuwland wrote: Martin v. Löwis wrote: That's not the full syntax. The full syntax is [ test for exprlist in testlist list-iter-opt ] where test can be an arbitrary expression: and, or, lambda, +, -, ... exprlist can be a list of expression, except for boolean and relational expressions (but I think this is further constrained semantically) testlist list a list of tests list-iter-opt is optional, and can be another for or if block Aren't these names a bit mixed up w.r.t. what's in that position? The names come directly from the grammar file (Grammar/Grammar) and thus have multiple uses. Basically ignore the actual names and just consider them placeholders. -Brett ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
Gareth McCaughan wrote: I'd like it, and my reason isn't just to save typing. There are two reasons. 1 Some bit of my brain is convinced that [x in stuff if condition] is the Right Syntax and keeps making me type it even though I know it doesn't work. 2 Seeing [x for x in stuff if condition] triggers my internal duplicated-stuff alarm, and it's distracting, in the same sort of way as it's distracting in C or C++ seeing The full syntax is: [ f(x) for x in seq if pred(x) ] being allowed to write 'x' instead of 'identity(x)' is already a shortcut, just as dropping the conditional part. Remember we're doing set theory stuff here. IMHO we should follow its notation conventions as much as we can. --eric ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
On Monday 2005-03-14 12:42, Eric Nieuwland wrote:
Gareth McCaughan wrote:
I'd like it, and my reason isn't just to save typing.
There are two reasons.
1 Some bit of my brain is convinced that [x in stuff if condition]
is the Right Syntax and keeps making me type it even though
I know it doesn't work.
2 Seeing [x for x in stuff if condition] triggers my internal
duplicated-stuff alarm, and it's distracting, in the same sort
of way as it's distracting in C or C++ seeing
The full syntax is:
[ f(x) for x in seq if pred(x) ]
being allowed to write 'x' instead of 'identity(x)' is already a
shortcut, just as dropping the conditional part.
Remember we're doing set theory stuff here. IMHO we should follow its
notation conventions as much as we can.
I'm well aware of what the full syntax is; being allowed to
write x instead of identity(x) is *not* a shortcut but
a perfectly straightforward unexceptional instance of the
usual syntax; list comprehensions already have neither the
syntax nor the semantics of set-theorists' comprehensions;
and in fact no set theorist would be at all troubled by seeing
{ x in S : predicate(x) }
which is the nearest equivalent in mathematical notation
for the abbreviated comprehension expressions being discussed.
Other than that, I quite agree :-).
--
g
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Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
[Nick Coghlan]
That 'x in seq' bit still shouts containment to me rather than
iteration, though.
Perhaps repurposing 'from':
(x from seq if f(x))
That rather breaks TOOWTDI though (since it is essentially new syntax
for a for loop). And I have other hopes for the meaning of (x from ()). . .
[Greg Ewing]
How about:
(for x in seq if f(x))
It still has the word 'for' in it and avoids mentioning
x more times than necessary.
Although I can't help feeling that it should be some
other word instead, such as
(all x in seq if f(x))
or
(every x in seq if f(x))
I doubt that we'll find a satisfactory solution for this issue. Here's why:
- We're only talking of a savings of 4 characters (plus two spaces) in
the best case, assuming the identifier can be a single letter (it's
scope is only the current expression anyway).
- Ping's proposal ('x in seq if f(x)') IMO loses for several reasons:
it would be a hugely ambiguous use of 'in', and would cut off a
possible future syntax for conditional expression(*): 'A if T else B'.
- The various improvements on Ping's proposal reduce the amount of
typing saved even more ('every' is actually longer than 'for x').
- Before anybody asks, I really do think the reason this is requested
at all is really just to save typing; there isn't the avoid double
evaluation argument that helped acceptance for assignment operators
(+= etc.), and I find redability is actually improved with 'for'.
(*) Pleas stop calling it 'ternary expression'. That doesn't explain
what it means. It's as if we were to refer to the + operator as
'binary expression'.
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
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Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
Nick Coghlan wrote: That 'x in seq' bit still shouts containment to me rather than iteration, though. Perhaps repurposing 'from': (x from seq if f(x)) That rather breaks TOOWTDI though (since it is essentially new syntax for a for loop). And I have other hopes for the meaning of (x from ()). . . How about: (for x in seq if f(x)) It still has the word 'for' in it and avoids mentioning x more times than necessary. Although I can't help feeling that it should be some other word instead, such as (all x in seq if f(x)) or (every x in seq if f(x)) -- Greg ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] comprehension abbreviation (was: Adding any() and all())
Jim Jewett wrote: Note that the last x shouldn't have to be x. [x in seq if f(x)] is by far my most common syntax error, and [x for x in seq if f(x)] is always what I want instead. That 'x in seq' bit still shouts containment to me rather than iteration, though. Perhaps repurposing 'from': (x from seq if f(x)) That rather breaks TOOWTDI though (since it is essentially new syntax for a for loop). And I have other hopes for the meaning of (x from ()). . . Cheers, Nick. -- Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia --- http://boredomandlaziness.skystorm.net ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
