Operator precedence problem

Random832 random832 at fastmail.com
Mon Jun 6 09:57:01 EDT 2016


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]


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