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Mon Apr 9 23:25:04 EDT 2001 · http://mail.python.org/pipermail/python-list/2001-April/089088.html

Carlos Alberto Reis Ribeiro <cribeiro at mail.inet.com.br> writes:

> >I'm not arguing against "programmer freedom".  I'm arguing for
> >features that reduce bugs without reducing power.

> That's the point. Because of the way Python works, it is almost impossible 
> to implement any kind of "attribute checking". My own code is filled with 
> this kind of construct. You can build new classes on the fly, make 
> composite objects, a whole lot of things that are nearly impossible to do 
> using other statically typed languages.

I'm not arguing that Python should be statically typed.  Just that it
is unfortunate that assignment automatically creates new variables.
Creating a new variable and assigning to an existing variable should
have been different operations.

A language that makes you declare a variable before using it doesn't
necessarily eliminate any power at all.  It just might make you type
a little bit more.  Such extra typing in some cases is surely worth
the extra safety, in my opinion.  Especially, since the lack of safety
in this case causes bugs that I see over and over again, and they are
often not always trivial to track down.

In the rare instances in which you want to set a variable even if it
hasn't been created yet, you can do something like this:

   try:
      set x = 3
   except NameError:
      let x = 3

> If you really think that this is a good idea (and I understand your
> position for some particular cases), put some checks on the
> __setattr__ of your class. It will trap all occurrences of new
> attributes being attached to the class instance. This is a quick
> example, by no means complete, that shows the concept:

But this doesn't fix the even more serious problem with local
variables.  Also my coworkers would kill me if I was doing this kind
of thing on all my classes, and it doesn't help when I have to work on
their code.

|>oug

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Class Variable Question