[Python-3000] Draft PEP for outer scopes

[Delaney, Timothy (Tim)]

Steven Bethard wrote:

> On 11/1/06, Ka-Ping Yee <python at zesty.ca> wrote:
>> I think a fairer survey example would be something like this:
>> 
>>     n = 1
>>     def f():
>>         n = 2
>>         def g():
>>             global n = 99
>>             return n
>>         g()
>> 
>>     f()
>>     print n
>> 
>> Which 'n' do you expect g() to change?
> 
> The only reason I didn't use that in the first place is that is seems
> extremely unlikely in real code.  Who uses the same name for a
> module-level binding and a function-local binding?
> 
> So yes, that's the corner case, but I contend that the corner case
> will almost never come up.

A much more likely corner case is (using existing syntax):

def f():
    def g()
        global n
        n = 99
        return n

    g()

f()
print n

What does this do? It depends on if f() has a binding of "n". If it
does, the above throws a NameError. If it doesn't, it prints 99.

For "nonlocal", this is a non-issue - it's a syntax error. But if we
reuse "global", the nested function is context-dependent.

If "global" were to change in Py3K to require an existing binding at the
time the "global" keyword was executed, this would then have the
semantics of "nonlocal" and be context-independent again. So I think any
proposal to reuse "global" has to include these semantics.

Tim Delaney