[Edu-sig] implementing summation notation (in Scheme & Python)

[list-python-edu@ccraig.org]

Kirby Urner <pdx4d@teleport.com> writes:

> In doing this post, I discovered what I consider rather strange
> behavior in the nested scopes department and posted about it to
> comp.lang.python.  Here's a copy of that post.  Maybe someone here
> can help rationalize this behavior:
> [problem with name binding in nested scopes]

>From PEP227:

   The name binding operations are argument declaration, assignment,
   class and function definition, import statements, for statements,
   and except clauses.  Each name binding occurs within a block
   defined by a class or function definition or at the module level
   (the top-level code block).

   If a name is bound anywhere within a code block, all uses of the
   name within the block are treated as references to the current
   block.  (Note: This can lead to errors when a name is used within a
   block before it is bound.)

augmented assignment is a 'name binding operation', which causes the
name 'a' to be used a a local variable in 'bar' rather than included
from the containing scope ('foo').  Note that this is done at compile
time, not runtime as you suggested (there isn't much of a difference
in Python, but there is one), because the function bar (like all
functions) was fully compiled before the call to it in foo.

-- 
Christopher A. Craig <list-python-edu@ccraig.org>
"Bah!  Puny, weak newsreaders!"- GNUS info, in reference to 'global' kills