[Python-ideas] Non-boolean return from __contains__
ianb at colorstudy.com
Mon Jul 26 18:09:18 CEST 2010
On Mon, Jul 26, 2010 at 9:53 AM, Oleg Broytman <phd at phd.pp.ru> wrote:
> On Mon, Jul 26, 2010 at 07:28:30AM -0700, Guido van Rossum wrote:
> > other odd ducks are 'and' and 'or', though in a pinch one can use '&'
> > and '|' for those. I forget in which camp 'not' falls.
> 'not' is like 'and' and 'or'. '~' is like '&' and '|'; its magic method
> is __invert__.
~ actually works okay (except for it reading poorly -- it's a rather obscure
operator), but & and | have precedence that makes them very error-prone in
my experience, e.g., (query.column == 'x' | query.column == 'y') becomes the
SQL "(column == ('x' OR column)) == 'y'".
I know overriding "and" and "or" has been discussed some time ago, though
I'm not sure what the exact reason is that it never went anywhere. I
remember it as one of those epic-and-boring comp.lang.python threads ;) One
obvious complication is that they are short-circuit operations. That is, "a
and b" must evaluate a, figure out if it is false, and if so then it returns
a. But "a or b" must evaluate a, figure out if it is TRUE, and if so then
returns a. So if there was anything like __and__ and __or__ it would have
to simply disable any short-circuiting.
Ian Bicking | http://blog.ianbicking.org
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