gistfile1.py

>>> b = 0
>>> def incB():
...   b += 1
... 
>>> c = []
>>> def addC():
...   c.append(1)
... 
>>> b
0
>>> c
[]
>>> incB()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in incB
UnboundLocalError: local variable 'b' referenced before assignment
>>> addC()
>>> c
[1]

Yep, the reason it happens makes sense. But it's the old 'const ptr vs ptr to const' issue. Seems like we should be able to avoid that by now in high level languages. I'd actually prefer if 'global' was required to access the external scope.

Heh I wouldn't mind that either since I absolutely hate globals in code that are not constants declared in ALL_CAPS. I really doubt that'd fly if suggested on python-ideas@ though. ;)