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Re: Eval of expr with 'or' and 'and' within

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On 2013-06-14 10:50, Nick the Gr33k wrote:
> I started another thread because the last one was !@#$'ed up by irrelevant
> replies and was difficult to jeep track.
>
>  >>> name="abcd"
>  >>> month="efgh"
>  >>> year="ijkl"
>
>  >>> print(name or month or year)
> abcd
>
> Can understand that, it takes the first string out of the 3 strings that has a
> truthy value.
>
>  >>> print("k" in (name and month and year))
> True
>
> No clue. since the expression in parenthesis returns 'abcd' how can 'k'
> contained within 'abcd' ?
>
>  >>> print(name and month and year)
> ijkl
>
> Seems here is returning the last string out of 3 strings, but have no clue why
> Python doing this.
>
>  >>> print("k" in (name and month and year))
> True
>  >>>
>
> yes, since expression returns 'ijkl', then the in operator can detect the 'k'
> character within the returned string.
>
> This is all iw ant to know.

This is all you need to read:

   http://docs.python.org/2/reference/expressions.html#boolean-operations

Note the difference between how "or" and "and" each short-circuit. That is why 
the (name or month or year) returns the first truthy value while (name and month 
and year) returns the last truthy value. When "or" finds the first truthy value, 
it can stop looking since the whole expression must be truthy no matter what the 
values are after it. "and" cannot stop looking until it finds a falsy value or 
runs out of values to look at.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-14 12:50 +0300
  Re: Eval of expr with 'or' and 'and' within Fábio Santos <fabiosantosart@gmail.com> - 2013-06-14 11:03 +0100
  Re: Eval of expr with 'or' and 'and' within Robert Kern <robert.kern@gmail.com> - 2013-06-14 11:14 +0100
    Re: Eval of expr with 'or' and 'and' within Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-14 16:09 +0000
      Re: Eval of expr with 'or' and 'and' within rusi <rustompmody@gmail.com> - 2013-06-14 09:21 -0700
      Re: Eval of expr with 'or' and 'and' within Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-06-14 20:03 +0200
        Re: Eval of expr with 'or' and 'and' within rusi <rustompmody@gmail.com> - 2013-06-14 11:37 -0700
          Re: Eval of expr with 'or' and 'and' within Joshua Landau <joshua.landau.ws@gmail.com> - 2013-06-14 19:47 +0100
      Re: Eval of expr with 'or' and 'and' within alex23 <wuwei23@gmail.com> - 2013-06-14 23:50 -0700
        Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-15 10:04 +0300
          Re: Eval of expr with 'or' and 'and' within Denis McMahon <denismfmcmahon@gmail.com> - 2013-06-15 07:49 +0000
            Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-15 10:59 +0300
  Re: Eval of expr with 'or' and 'and' within Grant Edwards <invalid@invalid.invalid> - 2013-06-14 14:49 +0000
    Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-14 18:16 +0300
      Re: Eval of expr with 'or' and 'and' within Nobody <nobody@nowhere.com> - 2013-06-14 17:42 +0100
        Re: Eval of expr with 'or' and 'and' within Grant Edwards <invalid@invalid.invalid> - 2013-06-14 19:30 +0000
          Re: Eval of expr with 'or' and 'and' within Nobody <nobody@nowhere.com> - 2013-06-15 00:02 +0100
        Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-15 10:57 +0300
  Re: Eval of expr with 'or' and 'and' within Michael Torrie <torriem@gmail.com> - 2013-06-14 10:29 -0600
    Re: Eval of expr with 'or' and 'and' within Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-14 16:49 +0000
      Re: Eval of expr with 'or' and 'and' within Michael Torrie <torriem@gmail.com> - 2013-06-14 11:28 -0600
      Re: Eval of expr with 'or' and 'and' within MRAB <python@mrabarnett.plus.com> - 2013-06-14 18:49 +0100
      Re: Eval of expr with 'or' and 'and' within Chris Angelico <rosuav@gmail.com> - 2013-06-15 03:56 +1000
        Re: Eval of expr with 'or' and 'and' within Grant Edwards <invalid@invalid.invalid> - 2013-06-14 19:33 +0000
          Re: Eval of expr with 'or' and 'and' within Chris Angelico <rosuav@gmail.com> - 2013-06-15 09:56 +1000
        Re: Eval of expr with 'or' and 'and' within Nobody <nobody@nowhere.com> - 2013-06-15 00:09 +0100
          Re: Eval of expr with 'or' and 'and' within Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-15 01:34 +0000
            Re: Eval of expr with 'or' and 'and' within Cameron Simpson <cs@zip.com.au> - 2013-06-15 12:03 +1000
              NANs [was Re: Eval of expr with 'or' and 'and' within] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-15 04:22 +0000
            Re: Eval of expr with 'or' and 'and' within Chris Angelico <rosuav@gmail.com> - 2013-06-15 12:21 +1000
      Re: Eval of expr with 'or' and 'and' within Nobody <nobody@nowhere.com> - 2013-06-15 00:06 +0100
        Re: Eval of expr with 'or' and 'and' within MRAB <python@mrabarnett.plus.com> - 2013-06-15 01:26 +0100
  Re: Eval of expr with 'or' and 'and' within Benjamin Kaplan <benjamin.kaplan@case.edu> - 2013-06-14 09:47 -0700
    Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-14 20:01 +0300
      Re: Eval of expr with 'or' and 'and' within Robert Kern <robert.kern@gmail.com> - 2013-06-14 18:27 +0100
      Re: Eval of expr with 'or' and 'and' within Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-06-14 22:05 +0300
      Re: Eval of expr with 'or' and 'and' within Grant Edwards <invalid@invalid.invalid> - 2013-06-14 19:36 +0000
  Re: Eval of expr with 'or' and 'and' within Cameron Simpson <cs@zip.com.au> - 2013-06-15 10:14 +1000
    Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-15 11:20 +0300
      Re: Eval of expr with 'or' and 'and' within Lele Gaifax <lele@metapensiero.it> - 2013-06-15 11:48 +0200
        Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-15 16:24 +0300
        Re: Eval of expr with 'or' and 'and' within Nick the Gr33k <support@superhost.gr> - 2013-06-15 16:28 +0300

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