[Tutor] learning nested functions

[Dave Angel]

On 07/08/2013 02:26 AM, Tim Hanson wrote:
> In  the first Lutz book, I am learning about nested functions.
>
> Here's the book's example demonstrating global scope:
>>>> def f1():
> 	x=88
> 	def f2():
> 		print(x)
> 	f2()
>
> 	
>>>> f1()
> 88
>

But that's not global scope, it's non-local scope.  Global would be if 
you were referencing a symbol defined at top-level.

> No problem so far.  I made a change and ran it again:
>
>>>> def f1():
> 	x=88
> 	def f2():
> 		print(x)
> 		x=99
> 		print(x)
> 	f2()
>
> 	
>>>> f1()
> Traceback (most recent call last):
>    File "<pyshell#11>", line 1, in <module>
>      f1()
>    File "<pyshell#10>", line 7, in f1
>      f2()
>    File "<pyshell#10>", line 4, in f2
>      print(x)
> UnboundLocalError: local variable 'x' referenced before assignment
>
> This doesn't work.  To my mind,in f2() I first print(x) then assign a variable
> with the same name in the local scope, then print the changed x.  Why doesn't
> this work?

As Hugo says, a function is compiled into a single entity, and within 
that entity, a given name is either local or not.  It's decided by the 
presence (anywhere in the function) of an assignment, or a with 
statement, or maybe other name-binding statements.



-- 
DaveA