On Feb 24, 8:25 am, Neil Cerutti <ne...@norwich.edu> wrote:
> > What Python needs is some constant that can be compared to ANY
> > numeric type and that constant will ALWAYS be larger!
> What's the point of that?
> The only time I've naively pined for such a thing is when
> misapplying C idioms for finding a minimum value.
The best use case is for default arguments to constructors or func/
meths. If you set the argument to INFINITY instead of -1 (or some
other dumb string value to mean "unlimited") you can omit a useless
conditional block later. Observe:
if maxlength == -1 # unlimited length:
keep_going()
elif len(object) < maxlength:
stop() # because we reached the limit
I see tons and tons of old Python code that uses -1 as an "unlimited"
value, where positive numbers are meant to constrain dome value. I
have always found that to be intuitive; hence my question.
On Feb 24, 9:21 am, Mel Wilson <mwil...@the-wire.com> wrote:
> Easily fixed:
> [...snip code...]
Yes i could write my own implementation of INFINITY if i wanted,
although i would have returned True and False as apposed to 1 and 0
AND used the identifiers Infinity and Infinitesimal, but i digress :-
P.
However, INFINITY is something i believe a language should provide;
which python does, albeit inconsistently.
> Yes i could write my own implementation of INFINITY if i wanted,
> although i would have returned True and False as apposed to 1 and 0
> AND used the identifiers Infinity and Infinitesimal, but i digress :-
> P.
> However, INFINITY is something i believe a language should provide;
> which python does, albeit inconsistently.
How do you represent infinity as an binary integer number? Or are you
suggesting that the integer type (class) be modified to allow an
"infinity" state that really isn't a number at all (could not be stored
as a integer in C)?
Float is a different story because IEEE does define a binary
representation of infinity in the floating-point specification.
I know of no language that has any form of representation of infinity
for integers mainly because there's no way to represent infinity as a
standard twos-compliment binary number. In a language that deals
directly with types in memory such as C, having an infinity
representation would be possible but would make simple math really hard,
and much slower.
All this reminds me of the original cray supercomputers. They didn't
use twos compliment for integers so they had two representations of zero
(+0 and -0). Made programming a bit tricky. When asked why the cray
didn't just do two's compliment like everyone else, Seymour Cray
responded that when the computer was designed he simply didn't know
about twos compliment.
> On 02/24/2012 08:34 AM, Rick Johnson wrote:
>> Yes i could write my own implementation of INFINITY if i wanted,
>> although i would have returned True and False as apposed to 1 and 0
>> AND used the identifiers Infinity and Infinitesimal, but i digress :-
>> P.
>> However, INFINITY is something i believe a language should provide;
>> which python does, albeit inconsistently.
> How do you represent infinity as an binary integer number? Or are you
> suggesting that the integer type (class) be modified to allow an
> "infinity" state that really isn't a number at all (could not be stored
> as a integer in C)?
The C integer bit doesn't matter since e.g.
>>> a=1000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000
>>> a
100000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000L
And no, I'm not going to calculate how much memory I'd need to store a string that's this long :)
> Float is a different story because IEEE does define a binary
> representation of infinity in the floating-point specification.
> I know of no language that has any form of representation of infinity
> for integers mainly because there's no way to represent infinity as a
> standard twos-compliment binary number. In a language that deals
> directly with types in memory such as C, having an infinity
> representation would be possible but would make simple math really hard,
> and much slower.
> All this reminds me of the original cray supercomputers. They didn't
> use twos compliment for integers so they had two representations of zero
> (+0 and -0). Made programming a bit tricky. When asked why the cray
> didn't just do two's compliment like everyone else, Seymour Cray
> responded that when the computer was designed he simply didn't know
> about twos compliment.
On Fri, Feb 24, 2012 at 9:25 AM, Neil Cerutti <ne...@norwich.edu> wrote:
> The only time I've naively pined for such a thing is when
> misapplying C idioms for finding a minimum value.
> Python provides an excellent min implementation to use instead.
min can be a little inconvenient. As soon as anything complicated has
to be done during the min expression, you need to switch to using
something else for sanity's sake. In that vein, I do actually
sometimes use float('inf') (for numbers), or a custom max/min object.
----
Silly and completely nonserious addendum:
Forgive me, I have spoken in error! min is the one true way, for you
can still do it with a little wrangling, as follows:
@operator.itemgetter(1)
@min
@apply
def closest_object():
for x in xrange(board_width)
for y in xrange(board_height):
try:
entity = board.get_entity(x, y)
except EntityNotFound:
pass
else:
yield distance(player.pos, entity.pos), entity
On Fri, 24 Feb 2012 09:23:08 -0700, Michael Torrie wrote:
> All this reminds me of the original cray supercomputers. They didn't
> use twos compliment for integers so they had two representations of zero
> (+0 and -0). Made programming a bit tricky.
While there is only one integer zero, I would like to point out that in floating point, there are usually two zeroes, -0.0 and +0.0, and that this is by design and a feature, not an accident or a bug.
Well-written floating point functions should keep the sign when they underflow, e.g.:
py> 1e-200 * 1e-200
0.0
py> 1e-200 * -1e-200
-0.0
and well-written functions should honour those separate zeroes because sometimes it makes a difference.
> a=1000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000
> >>> a
> 100000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000L
> And no, I'm not going to calculate how much memory I'd need to store a > string that's this long :)
Sure but that doesn't answer the question posed. How does Rick plan to
represent an infinite integer? Obviously you've shown that with an
infinite amount of memory we could do it quite easily. But baring that,
how does Rick suggest we should represent an infinite integer?
On Sat, Feb 25, 2012 at 10:16 AM, Michael Torrie <torr...@gmail.com> wrote:
> Sure but that doesn't answer the question posed. How does Rick plan to
> represent an infinite integer? Obviously you've shown that with an
> infinite amount of memory we could do it quite easily. But baring that,
> how does Rick suggest we should represent an infinite integer?
Barring a suggestion from Rick, I think we should define the number 8
to be greater than all other integers. After all, Rick's very much in
favour of evolution, and what would better depict the evolution of
this glorious language than this notation, showing that the infinity
symbol is now walking erect!
> On 02/24/2012 09:59 AM, Mark Lawrence wrote:
>> The C integer bit doesn't matter since e.g.
>> a=1000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000
>> >>> a
>> 100000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000L
>> And no, I'm not going to calculate how much memory I'd need to store a
>> string that's this long :)
> Sure but that doesn't answer the question posed. How does Rick plan to
> represent an infinite integer? Obviously you've shown that with an
> infinite amount of memory we could do it quite easily. But baring that,
> how does Rick suggest we should represent an infinite integer?
I understand that a Python integer can run to infinity. Quite how the illustrious rr manages to test for the length of a string that's already used all of the memory on his system has baffled me, but I'm sure that all the people who frequent this list with their Phds, MScs or whatever will soon correct me.
> On 02/24/2012 09:59 AM, Mark Lawrence wrote:
>> The C integer bit doesn't matter since e.g.
>> a=1000000000000000000000000000000000000000000000000000000000000000000000000 0000000000000000000000000000000000000000000000
>> >>> a
>> 100000000000000000000000000000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000L
>> And no, I'm not going to calculate how much memory I'd need to store a
>> string that's this long :)
> Sure but that doesn't answer the question posed. How does Rick plan to
> represent an infinite integer? Obviously you've shown that with an
> infinite amount of memory we could do it quite easily. But baring that,
> how does Rick suggest we should represent an infinite integer?
We already have arbitrarily long ints, so there could be a special
infinite int singleton (actually, 2 of them, one positive, the other
negative).
> We already have arbitrarily long ints, so there could be a special
> infinite int singleton (actually, 2 of them, one positive, the other
> negative).
Seconded. Although would a wish request to bugs.python.org saying "Allow storage of the integer infinity" make any sense to the developers? :P
-- Fayaz Yusuf Khan
Cloud developer and architect
Dexetra SS, Bangalore, India
fayaz.yusuf.khan_AT_gmail_DOT_com
fayaz_AT_dexetra_DOT_com
+91-9746-830-823
<jeanpierr...@gmail.com> wrote:
> On Fri, Feb 24, 2012 at 9:25 AM, Neil Cerutti <ne...@norwich.edu> wrote:
>> The only time I've naively pined for such a thing is when
>> misapplying C idioms for finding a minimum value.
>> Python provides an excellent min implementation to use instead.
> min can be a little inconvenient. As soon as anything complicated has
> to be done during the min expression, you need to switch to using
> something else for sanity's sake. In that vein, I do actually
> sometimes use float('inf') (for numbers), or a custom max/min object.
> ----
> Silly and completely nonserious addendum:
> Forgive me, I have spoken in error! min is the one true way, for you
> can still do it with a little wrangling, as follows:
> @operator.itemgetter(1)
> @min
> @apply
> def closest_object():
> for x in xrange(board_width)
> for y in xrange(board_height):
> try:
> entity = board.get_entity(x, y)
> except EntityNotFound:
> pass
> else:
> yield distance(player.pos, entity.pos), entity
Cute, but what's so terrible about:
def all_entities():
for x in xrange(board_width):
for y in xrange(board_height):
try:
yield board.get_entity(x, y)
except EntityNotFound:
pass
On Sat, 25 Feb 2012 06:52:09 +0530, Fayaz Yusuf Khan wrote:
> On Saturday 25 Feb 2012 12:37:58 AM MRAB wrote:
>> We already have arbitrarily long ints, so there could be a special
>> infinite int singleton (actually, 2 of them, one positive, the other
>> negative).
> Seconded. Although would a wish request to bugs.python.org saying "Allow
> storage of the integer infinity" make any sense to the developers? :P
If you explained it as a pair of special int values, INF and -INF, rather than the storage of an infinite-sized integer, it would make perfect sense.
But it would also be rejected, and rightly so, as unnecessary complexity for the int type. There are already Decimal and float infinities, just use one of them. Or make your own, it's not difficult. Publish it on ActiveState, and if people flock to use it, then you will have a good argument that this is useful and should be part of the Python built-ins.
> What Python needs is some constant that can be compared to ANY numeric
> type and that constant will ALWAYS be larger!
If there is no limit for len(string), why not simply use
# get_limit() returns None if there is no limit
maxlength = get_limit()
if maxlength and (len(string) <= maxlength):
allow_passage()
else:
deny_passage()
> We already have arbitrarily long ints, so there could be a special
> infinite int singleton (actually, 2 of them, one positive, the other
> negative).
>> What Python needs is some constant that can be compared to ANY numeric
>> type and that constant will ALWAYS be larger!
> If there is no limit for len(string), why not simply use
> # get_limit() returns None if there is no limit
> maxlength = get_limit()
> if maxlength and (len(string)<= maxlength):
> allow_passage()
> else:
> deny_passage()
That should be:
if maxlength is not None and len(string) <= maxlength:
On Feb 24, 6:35 pm, Mark Lawrence <breamore...@yahoo.co.uk> wrote:
> I understand that a Python integer can run to infinity. Quite how the
> illustrious rr manages to test for the length of a string that's already
> used all of the memory on his system has baffled me,
When did i ever say that i would need a string who's length is
INFINITY? In fact, i don't. My example was just that, as SIMPLIFIED
example of the problem that was the genesis of my question. In my
"real world" problem, i don't expect the string to EVER be more than
double digits in length. But as any good programmer knows, you never
want to solve problems as globally as possible. I need to do
comparisons on strings now, but maybe integers later, or who knows.
INFINITY comparisons are useful in many places.
> but I'm sure that
> all the people who frequent this list with their Phds, MScs or whatever
> will soon correct me.
I don't believe you'd need a Phd to understand my problem.
