[Python-Dev] nonlocals() function?

[Nick Coghlan]

Steve Bonner wrote:
> What do we think of adding a built-in nonlocals() function that would
> be similar to globals() and locals()?  Like those functions, it would
> return a dictionary of variable names and their values. Since we now
> have the nonlocal statement, it would be consistent to keep the
> three scopes local/nonlocal/global with parallel capabilities. And it
> might sometimes be useful for code inside a nested function to see
> what variables are available at the enclosing level.

That isn't as easy as it may sound. locals() and globals() are each
single namespaces, while the nonlocals may actually span multiple
namespaces.

Python actually deals with this at compilation time and when the
function object is created - the interpreter knows the names of all the
nonlocal cells that need to be connected, and creates the appropriate
links to the cells in the outer scopes.

That situation doesn't translate well to dict-style access - while the
whole local namespace is readily accessible to the interpreter, as is a
pointer to the module namespace (for globals()), no such convenient data
source exists for the full set of possible nonlocal references from an
arbitrary function.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
---------------------------------------------------------------