Multiple comparisons in a single statement

[Stephen Tucker]

*Chris:*   Thank you for your confirmation.

*All:  *For the record, I meant that the tuples are all the same. The
tuples I have in mind contain strings, so the issue regarding the
"equality" (or otherwise) of 0 and 0.0 does not arise in my case.

Stephen.




To answer the question

On Thu, Mar 12, 2020 at 11:26 PM John Pote <johnpote at jptechnical.co.uk>
wrote:

>
> On 12/03/2020 18:08, Chris Angelico wrote:
> > On Fri, Mar 13, 2020 at 4:55 AM Stephen Tucker <stephen_tucker at sil.org>
> wrote:
> >> A quickie (I hope!).
> >>
> >> I am running Python 2.7.10 (and, yes, I know, support for it has been
> >> withdrawn.)
> > This is the same in Python 3.
> >
> >> I have three tuples that have been generated separately and I want to
> check
> >> that they are identical. all I want to do is to terminate the program
> and
> >> report an error if all three are not identical.
> >>
> >> My initial attempt to do this is to use logic of the form
> >>
> >> if not (mytup1 == mytup2 == mytup3):
> >>     raise Exception ("Tuples are not identical")
> >>
> >> I have tried this logic form in IDLE, and it seems to do what I want.
> >>
> >> Is this a reasonable way to do this, or is there a better way?
> >>
> > Yes absolutely! (Although, as a minor quibble, I would say "equal"
> > rather than "identical" here - when you talk about identity, you're
> > usually using the 'is' operator.) The meaning of chained comparisons
> > is broadly equivalent to comparing the middle one against the others
> > ("a==b==c" is "a==b and b==c"), which does the right thing here.
> >
> > It's slightly unusual to negate a query rather than using "!=", but it
> > makes good sense here.
>
> In case anyone thinks the original expr
>       not (mytup1 == mytup2 == mytup3)
> could be changed to
>       (mytup1 != mytup2!= mytup3)
> remember that applying De Morgan's theorem to the original expression
> would require the 'and' operation used in chained comparisons to change
> to an 'or' operation (Python always does the 'and' operation in chained
> comparisions). EG for simple integers instead of tuples,
>
>  >>> not (1==1==1)
> False
>  >>> not (2==1==1)
> True
>  >>> (1!=1!=1)
> False                          correct as before
>  >>> (2!=1!=1)
> False                          oops!
>
> John
>
> >
> > ChrisA
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>