proc A def/calls proc B: variable scoping rules.

[Steve Holden]

NevilleDNZ wrote:
> Can anyone explain why "begin B: 123" prints, but 456 doesn't?
> 
> $ /usr/bin/python2.3  x1x2.py
> begin A:
> Pre B: 123 456
> begin B: 123
> Traceback (most recent call last):
>   File "x1x2.py", line 13, in ?
>     A()
>   File "x1x2.py", line 11, in A
>     B()
>   File "x1x2.py", line 7, in B
>     print "begin B:",x1,x2
> UnboundLocalError: local variable 'x2' referenced before assignment
> 
> 
> $ cat x1x2.py
> #!/usr/bin/env python
> def A():
>   print "begin A:"
>   x1=123;
>   x2=456;
>   def B():
>     print "begin B:",x1,x2
>     x2 = x2 - 1; # comment out this line and script x1x2 magically
> works!!

Hardly surprising. This statement is an assignment to x2, which 
therefore becomes local to the function. Since no previous value has 
been assigned to this local, the exception occurs.

regards
  Steve
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