Re: Operator precedence problem

From	Random832 <random832@fastmail.com>
Newsgroups	comp.lang.python
Subject	Re: Operator precedence problem
Date	2016-06-06 09:57 -0400
Message-ID	<mailman.37.1465221424.2306.python-list@python.org> (permalink)
References	(3 earlier) <3ff71354-461a-4635-8d1a-c879243e39a8@googlegroups.com> <CAMQ2MsFfxF0wSL_y9tSFCoJ1BJ+GVqi2qJLTBzs7+BbGRjW3Bw@mail.gmail.com> <mailman.9.1465142763.2306.python-list@python.org> <2a577a90-3a39-4d8f-90fa-4a00fd4f06a3@googlegroups.com> <1465221421.1069788.629246361.60094337@webmail.messagingengine.com>

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On Mon, Jun 6, 2016, at 01:46, Lawrence D’Oliveiro wrote:
> On Monday, June 6, 2016 at 4:06:20 AM UTC+12, Uri Even-Chen wrote:
> > Never write expressions, such as  2 ** 3 ** 2 or even 2 * 4
> > + 5, without parentheses.
> 
> That leads to the code equivalent of
> <http://i.dailymail.co.uk/i/pix/2011/10/13/article-2048696-03F82C520000044D-302_634x332.jpg>.

Okay, can we settle on, as a principle, "the basic arithmetic operators
(not to include **)  are the only ones whose precedence can be presumed
to be obvious to all readers, and other expressions may/should have
parentheses to make it more clear, even when not strictly necessary to
the meaning of the expression"?

Sure, it's obvious to _me_ that << and >> have higher precedence than &
and |, and that "and" has a higher precedence than "or", but can I
assume the other people know this? And I don't know offhand the relative
precedence of non-conceptually-related groups of operators, except that
I'm pretty sure "and" and "or" have very low precedence.

[To keep this on-topic, let's assume that this discussion has a goal of
getting something along the lines of "always/sometimes/never use
"unnecessary" parentheses" into PEP7/PEP8. Speaking of, did you know
that C has lower precedence for the bitwise operators &^| than for
comparisons? That was something that tripped me up for a very long time
and undermined my confidence as to other aspects of the bitwise
operators]

Thread

Operator precedence problem ICT Ezy <ictezy@gmail.com> - 2016-06-04 23:53 -0700
  Re: Operator precedence problem Peter Otten <__peter__@web.de> - 2016-06-05 09:35 +0200
    Re: Operator precedence problem ICT Ezy <ictezy@gmail.com> - 2016-06-05 08:05 -0700
      Re: Operator precedence problem Uri Even-Chen <uri@speedy.net> - 2016-06-05 19:05 +0300
        Re: Operator precedence problem ICT Ezy <ictezy@gmail.com> - 2016-06-05 20:24 -0700
        Re: Operator precedence problem Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-05 22:46 -0700
          Re: Operator precedence problem Random832 <random832@fastmail.com> - 2016-06-06 09:57 -0400
            Re: Operator precedence problem Marko Rauhamaa <marko@pacujo.net> - 2016-06-06 17:22 +0300
              Re: Operator precedence problem Random832 <random832@fastmail.com> - 2016-06-06 10:35 -0400
                Re: Operator precedence problem Marko Rauhamaa <marko@pacujo.net> - 2016-06-06 17:55 +0300
              Re: Operator precedence problem Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-06-06 15:03 +0000
                Re: Operator precedence problem Marko Rauhamaa <marko@pacujo.net> - 2016-06-06 18:22 +0300
                Re: Operator precedence problem Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-06-06 15:27 +0000
                Re: Operator precedence problem Chris Angelico <rosuav@gmail.com> - 2016-06-07 01:57 +1000
                Re: Operator precedence problem Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-06-06 16:05 +0000
                Re: Operator precedence problem Chris Angelico <rosuav@gmail.com> - 2016-06-07 02:21 +1000
                Re: Operator precedence problem Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-06-06 17:02 +0000
                Re: Operator precedence problem Grant Edwards <grant.b.edwards@gmail.com> - 2016-06-06 16:51 +0000
              Re: Operator precedence problem Peter Otten <__peter__@web.de> - 2016-06-06 18:38 +0200
            Re: Operator precedence problem Steven D'Aprano <steve@pearwood.info> - 2016-06-07 03:07 +1000
              Re: Operator precedence problem Random832 <random832@fastmail.com> - 2016-06-06 14:44 -0400
                Re: Operator precedence problem Marko Rauhamaa <marko@pacujo.net> - 2016-06-06 21:49 +0300
              Re: Operator precedence problem MRAB <python@mrabarnett.plus.com> - 2016-06-06 20:17 +0100
                Re: Operator precedence problem Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-07 11:27 +1200
            Re: Operator precedence problem Rustom Mody <rustompmody@gmail.com> - 2016-06-06 10:14 -0700
              Re: Operator precedence problem Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-06-06 21:09 +0100
      Re: Operator precedence problem Michael Torrie <torriem@gmail.com> - 2016-06-05 17:47 -0600
        Re: Operator precedence problem ICT Ezy <ictezy@gmail.com> - 2016-06-05 20:23 -0700
  Re: Operator precedence problem Chris Angelico <rosuav@gmail.com> - 2016-06-06 02:24 +1000
    Re: Operator precedence problem Peter Pearson <pkpearson@nowhere.invalid> - 2016-06-06 16:58 +0000
      Re: Operator precedence problem Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-07 11:21 +1200
  Re: Operator precedence problem Random832 <random832@fastmail.com> - 2016-06-05 13:19 -0400
    Re: Operator precedence problem ICT Ezy <ictezy@gmail.com> - 2016-06-05 20:23 -0700
  Re: Operator precedence problem Gary Herron <gherron@digipen.edu> - 2016-06-05 00:04 -0700

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