Re: max(), sum(), next()
On Sat, Sep 6, 2008 at 12:57 AM, castironpi <[EMAIL PROTECTED]> wrote: > On Sep 5, 9:20 pm, "Manu Hack" <[EMAIL PROTECTED]> wrote: >> On Fri, Sep 5, 2008 at 1:04 PM, castironpi <[EMAIL PROTECTED]> wrote: >> > On Sep 5, 3:28 am, "Manu Hack" <[EMAIL PROTECTED]> wrote: >> >> On Thu, Sep 4, 2008 at 4:25 PM, castironpi <[EMAIL PROTECTED]> wrote: >> >> > On Sep 4, 2:42 pm, [EMAIL PROTECTED] wrote: >> >> >> David C. Ullrich: >> >> >> >> > At least in mathematics, the sum of the elements of >> >> >> > the empty set _is_ 0, while the maximum element of the >> >> >> > empty set is undefined. >> >> >> >> What do you think about my idea of adding that 'default' argument to >> >> >> the max()/min() functions? >> >> >> >> Bye, >> >> >> bearophile >> >> >> > For max and min, why can't you just add your argument to the set >> >> > itself? >> >> >> > The reason max([]) is undefined is that max( S ) is in S. >> >> >> It makes sense. >> >> >> >The reason sum([]) is 0 is that sum( [ x ] ) - x = 0. >> >> >> It doesn't make sense to me. What do you set x to? >> >> > For all x. >> >> But then how can you conclude sum([]) = 0 from there? It's way far >> from obvious. > > You can define sum([a1,a2,...,aN]) recursively as > sum([a1,a2,...a(N-1)])+aN. Call the sum sum([a1,a2,...,aN]) "X", then > subtract aN. > > sum([a1,a2,...a(N-1)])+aN=X > sum([a1,a2,...a(N-1)])+aN-aN=X-aN > > For N=2, we have: > > sum([a1,a2])=X > sum([a1,a2])-a2=X-a2 > sum([a1,a2])-a2-a1=X-a2-a1 > > Since X= a1+ a2, replace X. > > sum([a1,a2])-a2-a1=(a1+a2)-a2-a1 > > Or, > > sum([a1,a2])-a2-a1=0 > > Apply the recursive definition: > > sum([a1])+a2-a2-a1=0 > > And again: > > sum([])+a1+a2-a2-a1=0 > > And we have: > > sum([])=0. It makes more sense now, I just wanted to point out that only with sum([x]) = x, you can't get sum([]) = 0. -- http://mail.python.org/mailman/listinfo/python-list
Re: max(), sum(), next()
On Fri, Sep 5, 2008 at 11:45 PM, Steven D'Aprano <[EMAIL PROTECTED]> wrote: > On Fri, 05 Sep 2008 22:20:06 -0400, Manu Hack wrote: > >> On Fri, Sep 5, 2008 at 1:04 PM, castironpi <[EMAIL PROTECTED]> wrote: > ... >>>> >The reason sum([]) is 0 is that sum( [ x ] ) - x = 0. >>>> >>>> It doesn't make sense to me. What do you set x to? >>> >>> For all x. >> >> But then how can you conclude sum([]) = 0 from there? It's way far from >> obvious. > > I think Castironpi's reasoning is to imagine taking sum([x])-x for *any* > possible x (where subtraction and addition is defined). Naturally you > always get 0. > > Now replace x by *nothing at all* and you get: > > sum([]) "subtract nothing at all" = 0 > > I think that this is a reasonable way to *informally* think about the > question, but it's not mathematically sound, because if you replace x > with "nothing at all" you either get: > > sum([]) - = 0 > > which is invalid (only one operand to the subtraction operator), or you > get: > > sum([0]) - 0 = 0 > > which doesn't involve an empty list. What castironpi seems to be doing is > replacing "nothing at all" with, er, nothing at all in one place, and > zero in the other. And that's what makes it unsound and only suitable as > an informal argument. Actually it's even more natural to state sum([x]) = x, and this way you can never conclude that sum([]) = 0 from there. -- http://mail.python.org/mailman/listinfo/python-list
Re: max(), sum(), next()
On Fri, Sep 5, 2008 at 1:04 PM, castironpi <[EMAIL PROTECTED]> wrote: > On Sep 5, 3:28 am, "Manu Hack" <[EMAIL PROTECTED]> wrote: >> On Thu, Sep 4, 2008 at 4:25 PM, castironpi <[EMAIL PROTECTED]> wrote: >> > On Sep 4, 2:42 pm, [EMAIL PROTECTED] wrote: >> >> David C. Ullrich: >> >> >> > At least in mathematics, the sum of the elements of >> >> > the empty set _is_ 0, while the maximum element of the >> >> > empty set is undefined. >> >> >> What do you think about my idea of adding that 'default' argument to >> >> the max()/min() functions? >> >> >> Bye, >> >> bearophile >> >> > For max and min, why can't you just add your argument to the set >> > itself? >> >> > The reason max([]) is undefined is that max( S ) is in S. >> >> It makes sense. >> >> >The reason sum([]) is 0 is that sum( [ x ] ) - x = 0. >> >> It doesn't make sense to me. What do you set x to? > > For all x. But then how can you conclude sum([]) = 0 from there? It's way far from obvious. -- http://mail.python.org/mailman/listinfo/python-list
Re: max(), sum(), next()
On Thu, Sep 4, 2008 at 4:25 PM, castironpi <[EMAIL PROTECTED]> wrote: > On Sep 4, 2:42 pm, [EMAIL PROTECTED] wrote: >> David C. Ullrich: >> >> > At least in mathematics, the sum of the elements of >> > the empty set _is_ 0, while the maximum element of the >> > empty set is undefined. >> >> What do you think about my idea of adding that 'default' argument to >> the max()/min() functions? >> >> Bye, >> bearophile > > For max and min, why can't you just add your argument to the set > itself? > > The reason max([]) is undefined is that max( S ) is in S. It makes sense. >The reason sum([]) is 0 is that sum( [ x ] ) - x = 0. It doesn't make sense to me. What do you set x to? -- http://mail.python.org/mailman/listinfo/python-list
Re: fromfile error on windows, not mac
On Wed, Jul 23, 2008 at 3:37 PM, jadamwil <[EMAIL PROTECTED]> wrote: > I found the problem: I thought it was opening in binary mode on BOTH > windows and the mac, but on windows I passed "rb" with double quotes, > not 'rb' with single quotes to the open file function. Changing it to > 'rb' fixed it. > > by the way, anyone could explain why changing to single quote makes a difference? >>> "rb" == 'rb' True -- http://mail.python.org/mailman/listinfo/python-list
Re: Rpy Module
On Fri, May 16, 2008 at 6:14 PM, Mike P <[EMAIL PROTECTED]>
wrote:
> Hi experts,
>
> I've just seen there is an R module, what i can't see easily is if you
> can / how to import other modules for R into the Rpy module
>
> Can anyone advise on this?
Say if you want to use Hmisc within rpy,
import rpy
rpy.r.library('Hmisc')
Manu
--
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Re: Official IRC channel for Python?
On 23 Feb 2008 22:21:59 -0800, Paul Rubin <"http://phr.cx"@nospam.invalid> wrote: > "Manu Hack" <[EMAIL PROTECTED]> writes: > > > Really? maybe I'm been blocked from it... > > > thanks. > > > > > Maybe you need your nick name to be recognized. You need to register > > your nickname somewhere. > > On freenode, you need to register your nick in order to send private > messages, but you can join a channel with an unregistered nick. If > the nick is registered to someone else, you get a message saying to > identify (which in this situation actually means change nicks, since > you presumably don't have the password to identify as the other > person). > > Manu, what happens when you try to join? What happens if you change > nicks? Can you connect to freenode at all? Can you join other > channels? > -- For most of the channels there is not problem joining. Only the python channel I need to use message nickserv to identify in order to join. I'm not very into the irc thing so after the first time I register the nickname and then I don't seem to remember where I registered. LIke if I run /join python in irssi it gives #python You need to be identified to join that channel so I need to run /msg nickserv identify my_password and then I can join #python by running /join python. Manu > > > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
Re: Official IRC channel for Python?
On Sun, Feb 24, 2008 at 12:16 AM, js <[EMAIL PROTECTED]> wrote: > Really? maybe I'm been blocked from it... > thanks. Maybe you need your nick name to be recognized. You need to register your nickname somewhere. Manu -- http://mail.python.org/mailman/listinfo/python-list
property question
hi all, If I have a class A with A.x, A.y, A.z. A.y and A.z are property and in order to compute the value of them, A.y depends on A.x while A.z depends on A.y and A.x. If I call A.y, and A.z, the value A.y would be computed twice. Is there a smart way to avoid that as to A.y will be recomputed only if A.x has been changed? Now I can define more variables to keep track of what is changed but when there are more variables and the dependency becomes more involved it could be very complicated. Thanks a lot. Manu -- http://mail.python.org/mailman/listinfo/python-list
Re: RegEx question
On 10/4/07, Robert Dailey <[EMAIL PROTECTED]> wrote: > On 10/4/07, Adam Lanier <[EMAIL PROTECTED]> wrote: > > > > try @param\[(in|out)\] \w+ > > > > This didn't work either :( > > The tool using this regular expression (Comment Reflower for VS2005) May be > broken... > > -- > http://mail.python.org/mailman/listinfo/python-list > How about @param\[[i|o][n|u]t*\]\w+ ? -- http://mail.python.org/mailman/listinfo/python-list
