Python vars() global name error

Question

I\'m having a bit of trouble understanding what\'s going wrong with the following function:

def ness():
 pie=\'yum\'
 vars()[pie]=4
 print vars()[pie]
 print yum         


        

Answer 1

[Edit: I must be wrong here, since the 'exec' example works.]

As everyone points out, it's a bad idea to modify vars(). You can understand the error, though, by realizing that python in some sense doesn't "see" that "yum" is a local. "print yum" is still resolved as a global reference; this happens before any code is executed.

It's the same reason you get an UnboundLocalError from:

>>> y = 100
>>> def foo(x):
...   if x == 1:
...     y = 10
...   print y
... 
>>> foo(1)
10
>>> foo(2)
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 4, in foo
UnboundLocalError: local variable 'y' referenced before assignment