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

[NevilleDNZ]

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!!
    print "end B:",x1,x2
  print "Pre B:",x1,x2
  B()
  print "end A:",x1,x2
A()

$ /usr/bin/python2.3
Python 2.3.4 (#1, Mar 10 2006, 06:12:09)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>


$ /usr/bin/python2.3 -V
Python 2.3.4

$ /usr/local/bin/python2.4 -V
Python 2.4.2
$ /usr/local/bin/python2.4 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

# I compiled up 2.4 from the FC4 source, but 2.3 was from SL4.3
$ python -V
Python 2.4.2
$ python
Python 2.4.2 (#1, Aug 15 2006, 21:51:33)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
$