How to Detect Use of Unassigned(Undefined) Variable(Function)

[++imanshu]

    Is there a script/module to detect the use of unassigned
(undefined) variables(functions) in python. e.g. can I detect the
problem on line 3 automatically :-

i = 1
if i == 3:
    print o
print i

Thank You,
++imanshu
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