PEP 285: Adding a bool type

[Christian Tanzer]

Tim Peters <tim.one at comcast.net> wrote:

> [Christian Tanzer]
> > ...
> > If str and repr were to behave differently from each other, I'd expect
> > repr(True) to return "1" and str(True) to return "True". Interchanging
> > that seems strange.
>
> We try to ensure that eval(repr(x)) reproduce x whenever reasonably
> possible.  That best way to do that here is for repr(True) to return
> 'True'.

I understood the motivation for `repr(bool(1)) == "True"`.

What I wanted to say is that having repr return a readable result and
str return a result looking like an internal representation runs
counter to the usual conventions used for repr and str.

> > OTOH, I'm worried about backwards compatibility.
>
> That's the only reason for str(True) to return '1'.

In this case, I'd value consistency between repr/str higher than
backwards compatibility.

> How about str(True) return '1' but str(False) return 'False'? That's
> what a committee would compromise on <wink>.

Any self respecting committee would try harder and probably come up
with a really symmetric compromise:

    value    str      repr
    True     '1'      'True'
    False    'False'  '0'

<1.4. wink>

> > How will bool influence '__nonzero__'? Currently, Python insists that
> > '__nonzero__ should return an int'. Will this be changed to 'should
> > return a bool'?
>
> I hope so.
>
> > As that would break existing code, I hope not.
>
> No, "should" != "must".

Fine display of sophisticated hair splitting, but:

    >>> class Foo:
    ...   def __nonzero__(self): return None
    ...
    >>> f = Foo ()
    >>> not f
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
    TypeError: __nonzero__ should return an int
    >>>

I don't care about `should` vs. `must` as long as the new and improved
Python won't spit an exception at __nonzero__ code returning an int
instead of a bool.

> Guido won't call code that returns an int here broken, although he
> might call it deprecated, and leave you wondering when the hammer will
> drop <wink>.

Nice tease. But Guido's hammer with regard to future strictification
of bool is exactly what makes me uneasy.

-- 
Christian Tanzer                                         tanzer at swing.co.at
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