Mailman 3 August 2006 - Python-Dev

Re: [Python-Dev] Rounding float to int directly ...
by Nick Maclaren Aug. 4, 2006

Aug. 4, 2006

Ka-Ping Yee <python-dev(a)zesty.ca> wrote: > > That's my experience as well. In my opinion, the purpose of round() > is most commonly described as "to make an integer". So it should > yield an integer. Grrk. No, that logic is flawed. There are algorithms where the operation of rounding (or truncation) is needed, but where the value may be larger than can be held in an integer, and that is not an error. If the only rounding or truncation primitive converts to an integer, … [View More]

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segmentation fault in Python 2.5b3 (trunk:51066)
by Ralf Schmitt Aug. 4, 2006

Aug. 4, 2006

Hi all, I've been trying to port our software to python 2.5. unfortunately I'm getting constantly hit by segfaults. I've boiled it down to the following code: rs@schrotti:~/bug$ cat t.py import array class Indexer(object): maximumForwardSize = property(array.array.fromstring) rs@schrotti:~/bug$ python t.py Segmentation fault rs@schrotti:~/bug$ python Python 2.5b3 (trunk:51066, Aug 3 2006, 13:18:16) [GCC 4.0.3 (Ubuntu 4.0.3-1ubuntu5)] on linux2 Type "help", "copyright", "credits" or "… [View More]

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Rounding float to int directly (Re: struct module and coercing floats to integers)
by Jim Jewett Aug. 4, 2006

Aug. 4, 2006

Greg Ewing wrote: > The time isn't the main issue. The main issue > is that almost all the use cases for round() > involve doing an int() on it afterwards. At > least nobody has put forward an argument to > the contrary yet. Or, more accurately, they *should* involve an int afterwards, but often don't, because people expect round(something) to produce an integer. Looking only at the one-argument round() calls not surrounded by int(), I would bet that most are bugs rather than … [View More]

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Re: [Python-Dev] Rounding float to int directly ...
by Nick Maclaren Aug. 3, 2006

Aug. 3, 2006

James Y Knight <foom(a)fuhm.net> wrote: > > I'd be happy to see floats lose their __int__ method entirely, > replaced by an explicit truncate function. Come back Algol - all is forgiven :-) Yes, indeed. I have favoured that view for 35 years - anything that can lose information quietly should be explicit. tanzer(a)swing.co.at (Christian Tanzer) wrote: > Greg Ewing <greg.ewing(a)canterbury.ac.nz> wrote: > > > What's the feeling about this? If, e.g. int() … [View More]

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Re: [Python-Dev] Rounding float to int directly ...
by Nick Maclaren Aug. 3, 2006

Aug. 3, 2006

Greg Ewing <greg.ewing(a)canterbury.ac.nz> wrote: > > You should NOT be using binary floats for money > in the first place. Or floating-point at all, actually. But binary floating-point is definitely unsuited for such a use. > Pseudo-rounding to decimal places is not > the right way to do that. The right way is > to compare the difference to a tolerance. Right. Where the tolerance should be a combination of relative and absolute accuracy. 1.0e-300 should usually be … [View More]

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Re: [Python-Dev] Rounding float to int directly ...
by Michael Chermside Aug. 3, 2006

Aug. 3, 2006

Greg Ewing writes: > [I propose for Py3k that] builtin round() > to return an int, and have something somewhere > else, such as math.fround(), for round-to-float. +1. The need to convert float to int is pervasive. The need to round (binary) floats to integer (or other decimal) floats is _much_ less common. Furthermore, the need for "round to nearest int" is much more common than the need for "integer floor" (although as pointed out, each could be defined in terms of the other except … [View More]

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Re: [Python-Dev] Rounding float to int directly (Re: struct module and coercing floats to integers)
by Simon Burton Aug. 3, 2006

Aug. 3, 2006

On Wed, 2 Aug 2006 07:21:02 -0400 "Chermside, Michael" <mchermside(a)ingdirect.com> wrote: > > You wrote: > > (ie. I am wondering if truncating the float representation > > of an int always gives back the original int). > > Yes it does, because all integers that can be expressed as floats > can be expressed EXACTLY as floats. Yes, OK this makes sense. My point is that, regardless of this answer, as a python user I should not be worried by such details. At … [View More]

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Bad interaction of __index__ and sequence repeat
by Armin Rigo Aug. 3, 2006

Aug. 3, 2006

Hi, There is an oversight in the design of __index__() that only just surfaced :-( It is responsible for the following behavior, on a 32-bit machine with >= 2GB of RAM: >>> s = 'x' * (2**100) # works! >>> len(s) 2147483647 This is because PySequence_Repeat(v, w) works by applying w.__index__ in order to call v->sq_repeat. However, __index__ is defined to clip the result to fit in a Py_ssize_t. This means that the above problem exists with all … [View More]

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FW: using globals
by Werkhoven J.P. van (Sjaak) Aug. 2, 2006

Aug. 2, 2006

> Hi, > > I have got a problem with importing global variables. For instance I have > got two files: > > # t1.py #t2.py > > counter = 1 > > def counter_adder(filenr): def > show_adder(): > global counter import > t1 > counter+= 1 > print("adder is %d" % t1.counter) > if filenr == 1: > show_adder() > else: > import t2 > t2.show_adder() > > def show_adder(): > print("… [View More]

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Re: [Python-Dev] Rounding float to int directly ...
by Michael Chermside Aug. 2, 2006

Aug. 2, 2006

Nick Maclaren: > The "wobbling precision" effect may be overstated, > but is real, and gets worse the larger the base is. To the best of my > knowledge, that is almost the only way in which binary is more accurate > than decimal, in absolute terms, and it is a marginal difference. Okay, that makes sense. However, if I understand "wobbling precision" correctly (and it's a BIG if) then it refers to the fact that interpolating from the last digit of precision doesn't work so well (… [View More]

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