[Python-Dev] towards a faster Python

[Chris Reedy]

Neil Schemenauer wrote:

> The goal is that the compiler should be able to determine the scope of a
> name at compile time.  Code like the above does not allow that and so
> non-local names must be searched for in both globals and builtins at run
> time.  Unfortunately the warning is not bulletproof.  It's possible to
> modify the module dict directly and bypass the warning.  I'm not sure
> what to do about that. :-(

I think you might be looking for a test something like:

class special_dict(dict):
      """Special dictionary that doesn't allow changes to built-in names."""

      def __setitem__(self, key, value):
          if(key in self and hasattr(self[key], '__builtin_name__')
                         and key == self[key].__builtin_name__):
              raise_or_warn_changing_builtin(self, key, value)
          super(special_dict, self).__setitem__(key,value)

where __builtin_name__ is a new special attribute that would appear only
on built-in objects that aren't supposed to have their names changed.
The class special_dict would be used in situations where these kinds of
changes aren't supposed to occur. (Of course, I'd expect this to be
implemented in C in the guts of the interpreter for the obvious
performance reasons.)

This approach allows code like, for example:

     globals().myownrange = range
     ...
     for i in myownrange(5):
       ...

     Chris

P.S. I've been a lurker on this list for some time. I now propose to
climb back under my rock.

This is informal and not an official Mitretek Systems position.
Dr. Christopher L. Reedy, Senior Principal Software Engineer
Mitretek Systems
Email: creedy@mitretek.org