Re: [Python-Dev] == on object tests identity in 3.x

References	(5 earlier) <87a98ktjv7.fsf@uwakimon.sk.tsukuba.ac.jp> <CAPTjJmpvyvw81fY899mkuaui2d4u4dXr=2Vtz9z+JusOS=7DkA@mail.gmail.com> <8761j8thf5.fsf@uwakimon.sk.tsukuba.ac.jp> <20140708165745.GJ13014@ando> <53BC5053.1010904@jmunch.dk>
From	Ian Kelly <ian.g.kelly@gmail.com>
Date	2014-07-08 15:53 -0600
Subject	Re: [Python-Dev] == on object tests identity in 3.x
Newsgroups	comp.lang.python
Message-ID	<mailman.11663.1404856432.18130.python-list@python.org> (permalink)

Show all headers | View raw

On Tue, Jul 8, 2014 at 2:10 PM, Anders J. Munch <2014@jmunch.dk> wrote:
> Steven D'Aprano wrote:
>> - Keeping reflexivity for NANs would have implied some pretty nasty
>>    things, e.g. if log(-3) == log(-5), then -3 == -5.
>
>
>>>> log(-3)
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> ValueError: math domain error
>
> You were perhaps referring to the log functions in C and Fortran, not
> math.log?
> The tradeoffs are different in those languages, so choices the IEEE-754
> committee made with C and Fortran in mind may be less relevant for Python.

>>> import ctypes
>>> libm = ctypes.cdll.LoadLibrary("libm.so.6")
>>> log = libm.log
>>> log.argtypes = [ctypes.c_double]
>>> log.restype = ctypes.c_double
>>> log(-3)
nan
>>> log(-5)
nan
>>> log(-3) == log(-5)
False

Back to comp.lang.python | Previous | Next | Find similar | Unroll thread

Thread

Re: [Python-Dev] == on object tests identity in 3.x Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-08 15:53 -0600

csiph-web