lists of variables

[Steven D'Aprano]

On Sat, 20 Feb 2010 22:31:44 -0800, Carl Banks wrote:

> The one place where Python does have references is when accessing
> variables in an enclosing scope (not counting module-level).  

What makes you say that?

> But these
> references aren't objects, so you can't store them in a list, so it
> can't help you:

I don't even understand this. Your own example clearly shows that the are 
objects and you can store them in a list, so I have no understanding of 
what you mean.


> def f():
>     s = []
>     a = 1
>     def g():
>         print a

a is a name bound to an object which inherits a __str__ method, hence you 
can print it.

>         s.append(a)

a is bound to an object you can put in a list.

>     g() # prints 1
>     a = 2
>     g() # prints 2: g's a is a reference to f's a 
>     print s # prints [1,2] not [2,2]

Yes, you are correct that lexical scoping doesn't allow the OP to embed 
references to names in lists. I'm just confused why you think that 
lexical scoping is equivalent to references that can't be put in lists, 
or why you think this behaviour is any different from lexical scoping 
everywhere else?

# Instead of two scopes, f and g, use two scopes, the module (global)
# and local scope g:
s = []
a = 1
def g():
    print a
    s.append(a)

g() # prints 1
a = 2
g() # prints 2: g's a is a reference to the global a 
print s # prints [1,2] not [2,2]


There is no difference between lexical scoping between a function and a 
nested function, and the lexical scoping between the global namespace and 
a nested function.



-- 
Steven