None or 0

John Baxter jwbaxter at spamcop.net
Sat Sep 7 18:08:08 CEST 2002


In article <k7ip4-0p3.ln1 at junker.stroeder.com>,
 Michael Stroder <michael at stroeder.com> wrote:

>  >>> repr(0 or None)
> 'None'
>  >>> repr(None or 0)
> '0'
>  >>> repr('' or None)
> 'None'
>  >>> repr(None or '')
> "''"
>  >>>
> 
> Is it guaranteed to work like this or should that be avoided?

It seems very convenient to implement or (and and) by returning the 
first object which decides the answer.

My guess is that enough people are counting on the behavior that even if 
the underlying hardware or implementation language were to shift enough 
to make this implementation quite inconvenient, it would nonetheless 
survive.

Having said that, I tend not to like counting on it, because it 
stretches the extra-Python definition of the operators quite a bit.  
Particularly on the "and" side:

>>> print 5 and 1
1

Go into (English-speaking) classrooms, and you're going to hear chants 
of "5 and 1 is 6" not "5 and 1 is 1".

  --John



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