[Python-Dev] Passing floats to "i" parser marker

[Guido van Rossum]

> I was trying to suggest a parser marker for "accept whole
> numbers only", ie. floats without fraction, integers, subclasses
> of integers and other classes implementating __int__.

I'm still against that, for the reasons stated here:

> > Smarter people than you and me can disagree about that.  Personally, I
> > think that accepting floats with int values here is asking for
> > trouble: a calculation that returns a perfect int on one machine may
> > not do so on another, and hence a subtle portability problem is born.
> 
> True. I was thinking of cases where some external lib
> returns floats even for integers (e.g. database interface
> which return DECIMAL columns with scale 0 as floats --
> Zope converts these to integers; even though these can
> overflow). Now, you'll never see a float coming out of
> that interface with a non-0 fraction. With the change you'll
> also won't be able to pass the value as parameter to many
> thousand Python APIs anymore.
> 
> To work around this, the interface would have to be changed
> to apply a magic similar to the one Zope uses. But then
> you have a different problem: a change in data type based
> on a database type parameter.

This seems the burden of the database user in either case.  Trying to
compensate for this everywhere else in the language is wrong.

> Python 2.3a1:
>  >>> int(123478987123L)
> 123478987123L
> 
> Now, if I want to make sure that I can pass the value to
> "i" I'll have to add another check which makes sure that
> the int() return value is indeed a standard integer.

YADWTM (You Are Definitely Worrying Too Much :-).

--Guido van Rossum (home page: http://www.python.org/~guido/)