[Edu-sig] quantum instance

Kirby Urner urnerk at qwest.net
Mon Sep 19 18:18:44 CEST 2005

> My thought is that it is highly preferable - except in highly unusual
> circumstances - to call methods through method call syntax and to access
> attributes through attribute access syntax.  For reasons that are only
> obvious - we know better whether we are accessing something akin to a
> stored value or, in contrast, calling for something akin to a calculation 
> of a value. Which is information. Information is good.

And this is what I *don't* believe.  I think it's preferable to make mytri.A
(angle A) come across as an attribute, not a method call, even if I use a
method call to compute it on the fly.  

I want to be able to express user intuitions about what's a method and
what's an attribute drawing from a knowledge domain.  I don't want to
instruct a user in how Python must necessarily force a different view.

If the user wants to know whether a method is being invoked, the user should
just look at my source code (I think open source is highly preferable).

> Is the inclusion of properties into Python in fact to any extent as Kirby
> (and you, I think) seem to interpret it - an implicit vote on this matter?

Sure.  A lot of us think properties are a good idea.  *Every* feature added
to Python may be seen as an implicit "vote" although the precise process
whereby features get added is a little different from simple polling.

> But its cost is the extent to which it influences outcomes in unintended
> directions. If it was intended to influence toward greater use of the
> technique of calling methods through attribute access syntax, it is an
> unambiguous win.  Because it  - witness your statement above - undoubtedly
> does.

Yes, an unambiguous win.  Using attribute syntax to invoke methods is a good
thing in some circumstances (they don't even have to be "unusual"

I think you're misplacing your distrust.  If the source code is not
available at all, that's one issue.  There're lots of ways to hide
information in that case, including back doors, trap doors, whatever.  

But properties are not about hiding the source.  Properties are about making
the control panel more rational and stable from a user's point of view
(where the user may be oneself or another programmer).

> If one believes - as do I - that there was no such intention, then the
> addition of properties has suffered from the fate of having unintended
> consequences.  And in that sense cannot be viewed as an unambiguous win.
> Art

I believe encouraging the use of attribute syntax to invoke methods behind
the scenes is synonymous with managed access to class internals.  It's what
OO is encouraging and what Python is encouraging.  I don't subscribe to your
philosophy that we should avoid doing this.  I do it, and will continue to
do it, without apology.


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