[Python] 0 in (False,) // 0 == False

[Marco Mariani]

On 02/04/2010 12:25 PM, Alessandro Dentella wrote:

> Questa però non mi pare la risposta a "che bisogno c'è". Che non è una
> domana oziosa, è che immagino che ci *sia* bisogno in un modo che io ora non
> colgo. La domanda rifrasata sarebbe forse: quali sono le caratteristiche di
> un booleano che derivano da un intero?
>
> Riprendendo la tua risposta: che bisogno c'è che sia il più piccolo tipo
> *numerico* che porta informazione?
>   

Questo e' il pronunciamento di Guido al riguardo:

http://www.python.org/dev/peps/pep-0285/

6) Should bool inherit from int?

    => Yes.

       In an ideal world, bool might be better implemented as a
       separate integer type that knows how to perform mixed-mode
       arithmetic.  However, inheriting bool from int eases the
       implementation enormously (in part since all C code that calls
       PyInt_Check() will continue to work -- this returns true for
       subclasses of int).  Also, I believe this is right in terms of
       substitutability: code that requires an int can be fed a bool
       and it will behave the same as 0 or 1.  Code that requires a
       bool may not work when it is given an int; for example, 3 & 4
       is 0, but both 3 and 4 are true when considered as truth
       values.



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