[Python-Dev] Re: Re: Trinary Operators

[Jp Calderone]

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On Thu, Feb 06, 2003 at 09:43:40PM -0500, Terry Reedy wrote:
>=20
> [snip]
>=20
> I suspect that careful use of and/or will take care of half of real
> use cases for ternary (not 'trinary') operators.  IE, at least one of
> the expressions is either a non-null constant, as above, or an
> expression known to never be null when its condition is true.

  A semi-common case I have in my code is this:

class Foo:
    def __init__(self, x =3D None):
        if x is None:
            x =3D []
        self.x =3D x

  About half the time, I start to write the body of __init__ as this,
though:

    self.x =3D x is not None and x or []

  And then kick myself, for it potentially fails or produces unexpected
behavior when something passes [] into the function, and a reference to
*that* empty list is kept by the caller.  It might be convenient to be able
to write:

    self.x =3D [] if x is None else x

  So, this is a case where both expressions may evaluate to false, but the
identity of which is used as the final result is significant.

  otoh-I'm-happy-with-the-current-form'ly, Jp

--=20
#!/bin/bash
( LIST=3D(~/.netscape/sigs/*.sig)
  cat ${LIST[$(($RANDOM % ${#LIST[*]}))]}
  echo --$'\n' `uptime` ) > ~/.netscape/.signature
--=20
 up 53 days, 11:50, 8 users, load average: 0.13, 0.22, 0.19

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