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Re: I am never going to complain about Python again

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On 2013-10-10, MRAB <python@mrabarnett.plus.com> wrote:
> On 10/10/2013 16:57, Rotwang wrote:
>> On 10/10/2013 16:51, Neil Cerutti wrote:
>>> [...]
>>>
>>> Mixed arithmetic always promotes to the wider type (except in
>>> the case of complex numbers (Ha!)).
>>>
>>> r == c is equivalent to r == abs(c), which returns the magintude
>>> of the complex number.
>>
>> What?
>>
>>   >>> -1 == -1 + 0j
>> True
>>   >>> -1 == abs(-1 + 0j)
>> False
>>   >>> 1 == 0 + 1j
>> False
>>   >>> 1 == abs(0 + 1j)
>> True
>>
> Indeed.
>
> If r is real (float) and c is complex:
>
>      r == c means r == c.real and c.imag == 0.0

Woah. I thought I was going by what the docs say:

  Python fully supports mixed arithmetic: when a binary
  arithmetic operator has operands of different numeric types,
  the operand with the “narrower” type is widened to that of the
  other, where integer is narrower than floating point, which is
  narrower than complex. Comparisons between numbers of mixed
  type use the same rule. [2] The constructors int(), float(),
  and complex() can be used to produce numbers of a specific
  type.

[...]

  [2] Not for complex numbers. Instead convert to floats using
     abs() if appropriate.

I guess the "if appropriate" part eluded my eye. When *is* it
appropriate? Apparently not during an equal test.

>>> 5.0 == abs(3 + 4j)
False

-- 
Neil Cerutti

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I am never going to complain about Python again Steven D'Aprano <steve@pearwood.info> - 2013-10-10 04:36 +0000
  Re: I am never going to complain about Python again Chris Angelico <rosuav@gmail.com> - 2013-10-10 15:50 +1100
  Re: I am never going to complain about Python again Chris Rebert <clp2@rebertia.com> - 2013-10-09 22:26 -0700
  Re: I am never going to complain about Python again Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-10-10 06:39 +0100
  Re: I am never going to complain about Python again Christian Gollwitzer <auriocus@gmx.de> - 2013-10-10 08:41 +0200
  Re: I am never going to complain about Python again "Frank Millman" <frank@chagford.com> - 2013-10-10 10:23 +0200
  Re: I am never going to complain about Python again MRAB <python@mrabarnett.plus.com> - 2013-10-10 12:10 +0100
  Re: I am never going to complain about Python again Tim Chase <python.list@tim.thechases.com> - 2013-10-10 06:43 -0500
  Re: I am never going to complain about Python again "Frank Millman" <frank@chagford.com> - 2013-10-10 13:44 +0200
  Re: I am never going to complain about Python again Roy Smith <roy@panix.com> - 2013-10-10 09:09 -0400
    Re: I am never going to complain about Python again Neil Cerutti <neilc@norwich.edu> - 2013-10-10 15:51 +0000
      Re: I am never going to complain about Python again Rotwang <sg552@hotmail.co.uk> - 2013-10-10 16:57 +0100
        Re: I am never going to complain about Python again MRAB <python@mrabarnett.plus.com> - 2013-10-10 17:10 +0100
          Re: I am never going to complain about Python again Neil Cerutti <neilc@norwich.edu> - 2013-10-10 17:48 +0000
            Re: I am never going to complain about Python again Ian Kelly <ian.g.kelly@gmail.com> - 2013-10-10 12:35 -0600
              Re: I am never going to complain about Python again Neil Cerutti <neilc@norwich.edu> - 2013-10-10 18:49 +0000
            Re: I am never going to complain about Python again Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-10-10 20:47 +0100
              Re: I am never going to complain about Python again Neil Cerutti <neilc@norwich.edu> - 2013-10-10 19:54 +0000
            Re: I am never going to complain about Python again Cameron Simpson <cs@zip.com.au> - 2013-10-11 08:52 +1100
            Re: I am never going to complain about Python again Roy Smith <roy@panix.com> - 2013-10-10 20:07 -0400
              Is this the room for an argument? John Ladasky <john_ladasky@sbcglobal.net> - 2013-10-10 21:26 -0700
                Re: Is this the room for an argument? Roy Smith <roy@panix.com> - 2013-10-11 09:49 -0400
            Re: I am never going to complain about Python again Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-11 02:23 +0000
              Re: I am never going to complain about Python again Neil Cerutti <neilc@norwich.edu> - 2013-10-11 12:31 +0000
    Re: I am never going to complain about Python again Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-10-10 20:09 -0400
    Re: I am never going to complain about Python again Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-11 02:08 +0000
      Re: I am never going to complain about Python again Joshua Landau <joshua@landau.ws> - 2013-10-11 09:17 +0100
        Re: I am never going to complain about Python again Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-11 09:11 +0000
          Re: I am never going to complain about Python again Chris Angelico <rosuav@gmail.com> - 2013-10-11 20:52 +1100
          Re: I am never going to complain about Python again Joshua Landau <joshua@landau.ws> - 2013-10-11 17:56 +0100

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