Python 2.6.6 (r266:84292, Mar  3 2011, 15:11:07) 
[GCC 4.3.4] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> if foo: print 'foo declared'
... else: print 'foo not declared'
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'foo' is not defined
>>>