Nested scopes and class variables

From: Dave Benjamin (ramen_at_lackingtalent.com)
Date: 01/31/05 

Date: Mon, 31 Jan 2005 06:57:50 -0000

I ran into an odd little edge case while experimenting with functions that
create classes on the fly (don't ask me why):

>>> def f(x):
  ... class C(object):
  ... x = x
  ... print C.x
  ...
>>> f(5)
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
    File "<stdin>", line 2, in f
    File "<stdin>", line 3, in C
  NameError: name 'x' is not defined

"x" clearly is defined, but apparently Python is not looking at the nested
variable scope to find it. What's stranger is that if I rename the parameter
"x" to "y", the error goes away:

>>> def f(y):
  ... class C(object):
  ... x = y
  ... print C.x
  ...
>>> f(5)
  5

So, it's not like nested scopes aren't supported in the class block. Rather,
when it sees "x = x", it seems like Python is determining at that point that
"x" is a class variable, and refuses to search any further.

At the top-level, it works as expected:

>>> x = 5
>>> class C(object):
  ... x = x
  ...
>>> C.x
  5

Any implementation gurus have some insight into what's going on here? 

-- 
 .:[ dave benjamin: ramen/[sp00] -:- spoomusic.com -:- ramenfest.com ]:.
        "talking about music is like dancing about architecture."