Embedding questions

[Olaf Appelt]

Hi Fredrik,


thanks for your comments.

> > > Or you could go on and really abuse the language
> >
> > Shall I take that as a recommendation that I shouldn't use Python for
what I
> > need?
>
> nope.  you should think a bit more about your
> original problem.

OK. I need to know whether a given identifier was accessed (assigned a new
value or used in an expression).
I'm open for suggestions to achieve this other than by defining a set of
classes that carry that information:

class MyVariable
   def __init__ (self, default = 0)
      self.value = default
      self.readAccessed = 0
      self.writeAccessed = 0

   def assign (self, other)        # ugly
      self.value = other
      self.writeAccessed = 1

   def __add__ (self, other)
      r = MyVariable (self.value + other)
      self.readAccessed = 1
      return r

   #... all remaining arithmetic operators

Something like the above would result in what I need, I think. Except that
assignment would look bad.

Plan A was to define a set of classes like the above.
Let the user do some arithmetic with them, plus a few ifs, fors and whiles
and then examine the instances from C++ (retrieving value and state
information).

> if I understand things correctly, you want to
> set a variable to something, execute some user
> code, and then inspect that variable.  right?

Sounds right.

> okay, here's how to do that:
>
>     c = "my value"
>
>     namespace = {}
>     namespace["c"] = c
>
>     exec usercode in namespace
>
>     c = namespace["c"]
>
>     print c
>
> in other words, let the user change "c" to whatever
> he/she wants, and pick up the result afterwards.  if
> it's not the right type, convert it (if that's a reason-
> able thing to do).  otherwise, complain to the user.

OK, but I see two problems with this:
1. I still don't know whether it was accessed for read and/or write.
2. I can complain that the variable has an invalid value, but I can't tell
when exactly it changed to that value, which would be important for the
target audience (folks who know the problem domain, but not much about
programming).


Olaf