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Re: Not x.islower() has different output than x.isupper() in list output...

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From Chris Angelico <rosuav@gmail.com>
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Subject Re: Not x.islower() has different output than x.isupper() in list output...
Date Tue, 3 May 2016 20:25:17 +1000
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On Tue, May 3, 2016 at 8:00 PM,  <pavlovevidence@gmail.com> wrote:
>
> What you should have been expecting is a symmetry.  Say you have a string G.  islower(G) will return a certain result.  Now take every letter in G and swap the case, and call that string g.  isupper(g) will always return the same result is islower(G).
>
> More succinctly, for any string x, the following is always ture:
>
> islower(x) == isupper(swapcase(x))
>
> But that is not the same thing, and does not imply, as the following identity (which it turns out is not always true, as we've seen):
>
> islower(x) == not isupper(x)
>
>
> Another example of functions that behave like this are ispositive and isnegative.  The identity "ispositive(x) == isnegative(-x)" is always true.  However, "ispositive(x) == not isnegative(x)" is false if x == 0.
>

This assumes, of course, that there is a function swapcase which can
return a string with case inverted. I'm not sure such a function
exists.

ChrisA

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Thread

Re: Not x.islower() has different output than x.isupper() in list output... Christopher Reimer <christopher_reimer@icloud.com> - 2016-04-29 18:55 -0700
  Re: Not x.islower() has different output than x.isupper() in list   output... Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-04-30 17:47 +1200
  Re: Not x.islower() has different output than x.isupper() in list output... pavlovevidence@gmail.com - 2016-05-03 03:00 -0700
    Re: Not x.islower() has different output than x.isupper() in list output... Chris Angelico <rosuav@gmail.com> - 2016-05-03 20:25 +1000
      Re: Not x.islower() has different output than x.isupper() in list output... Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-05-03 14:25 +0300
        Re: Not x.islower() has different output than x.isupper() in list output... Chris Angelico <rosuav@gmail.com> - 2016-05-03 22:00 +1000
          Re: Not x.islower() has different output than x.isupper() in list output... DFS <nospam@dfs.com> - 2016-05-03 09:01 -0400
            Re: Not x.islower() has different output than x.isupper() in list output... Chris Angelico <rosuav@gmail.com> - 2016-05-03 23:13 +1000
              Re: Not x.islower() has different output than x.isupper() in list output... DFS <nospam@dfs.com> - 2016-05-03 09:19 -0400
                Re: Not x.islower() has different output than x.isupper() in list output... Chris Angelico <rosuav@gmail.com> - 2016-05-03 23:23 +1000
                Re: Not x.islower() has different output than x.isupper() in list output... Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-05-03 17:49 +0300
                Re: Not x.islower() has different output than x.isupper() in list output... DFS <nospam@dfs.com> - 2016-05-03 11:12 -0400
                Re: Not x.islower() has different output than x.isupper() in list output... Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-05-03 18:27 +0300
                Re: Not x.islower() has different output than x.isupper() in list output... Grant Edwards <grant.b.edwards@gmail.com> - 2016-05-03 15:42 +0000
                Re: Not x.islower() has different output than x.isupper() in list output... Terry Reedy <tjreedy@udel.edu> - 2016-05-03 12:37 -0400
                Re: Not x.islower() has different output than x.isupper() in list output... Steven D'Aprano <steve@pearwood.info> - 2016-05-04 13:28 +1000
                Re: Not x.islower() has different output than x.isupper() in list output... DFS <nospam@dfs.com> - 2016-05-04 10:09 -0400
                Re: Not x.islower() has different output than x.isupper() in list output... Chris Angelico <rosuav@gmail.com> - 2016-05-05 00:37 +1000
                Re: Not x.islower() has different output than x.isupper() in list output... Steven D'Aprano <steve@pearwood.info> - 2016-05-05 01:37 +1000
                Re: Not x.islower() has different output than x.isupper() in list output... DFS <nospam@dfs.com> - 2016-05-04 17:05 -0400
          Re: Not x.islower() has different output than x.isupper() in list output... Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-05-03 17:42 +0300
            Re: Not x.islower() has different output than x.isupper() in list output... Steven D'Aprano <steve@pearwood.info> - 2016-05-04 11:30 +1000
            Re: Not x.islower() has different output than x.isupper() in list output... Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-05-04 20:34 +1200
              Re: Not x.islower() has different output than x.isupper() in list output... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-05-04 19:06 +1000

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