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FixedPoint

Steve Holden sholden at holdenweb.com
Thu Feb 7 16:49:24 EST 2002 
"Mark McEahern" <marklists at mceahern.com> wrote in message
news:mailman.1013099052.17373.python-list at python.org...
> Steve Holden wrote:
> > Since the *intent* for None is that there should only ever be one
> > object of type None, the better test would be
> >
> >     if something is None
>
> Thanks, that's how I generally test for None--I didn't know the bit about
> "there should only ever be one."
>
Well, all I really meant was that binding another name or reference to None
doesn't create a new one. The ref man says in section 3.2

"""None
This type has a single value. There is a single object with this value. This
object is accessed through the built-in name None. It is used to signify the
absence of a value in many situations, e.g., it is returned from functions
that don't explicitly return anything. Its truth value is false. """

> However, you wrote:
>
> > which can easily be used without requiring any changes to FixedPoint.
>
> Well, sure, I could easily change my local copy of PyPgSql's PgSQL.py.
But
> it seems like in this case it makes more sense for me to change my local
> copy of FixedPoint.py.  Hmm, I'm having a hard time articulating *why*
> though.  I guess because we use PyPgSql more, it's actively maintained,
> etc.--I'm better off not maintaining our own branching of that code.
>
Oh, no, don't go changing other modules to fix this. Hadn't read your post
carefully enough to realize your problems were occurring with database
access.

> Of course, I could ask the PyPgSql folks not to test for None like that.
> But then they're going to say, "how's the bug actually happening?"  And
I'm
> going to have to tell them I'm sending a FixedPoint instance as a param to
> cursor.execute().  And *that* only works because I modified
FixedPoint.py's
> __repr__ to return str(self).  As you can tell, at the moment, I'm just
> flying by the seat of my pants trying to make something work.
>
Hmm. Really what's needed is an extension to PyPGSql's NUMBER type object,
but I don't think the maintainers will want to start getting involved in
special cases.

> > Good general rule: if Tim made it that way, it's supposed to be
> > that way :-)
>
> I tend to agree.  However, do you think he purposefully avoided making the
> code resilient to frippery like this?
>
> if FixedPoint(1.0) == None:
> ...
>
> Should it be resilient to code like that?  In the case of PyPgSql, one
could
> argue I'm using it incorrectly by passing it a FixedPoint to squirt into
the
> db.  But then that merely means I haven't framed my question correctly.
;-)
>
Equality to None is something pretty basic, and should be easy to test for.
You have my permission (like you need it) to fix FixedPoint :-0

I think we might admit that Tim's code was insufficiently polymorphic with
the built-in numeric types here.

but-he-knows-where-i-live-so-i'm-saying-it-quiet-ly y'rs  - steve
--
Consulting, training, speaking: http://www.holdenweb.com/
Author, Python Web Programming: http://pydish.holdenweb.com/pwp/

"This is Python.  We don't care much about theory, except where it
intersects with useful practice."  Aahz Maruch on c.l.py
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