Is vs Equality Operator

[Good Z]

Hello, 
I am having problem in using is. Here is what i am doing.

x=''
if x is None or x is '':
        return 1

The above statement does not return value 1.

If i changed the above check to 
if x == None or x == '':
        return 1
Now it works fine.

Any idea. What is happening here. I am using python 2.4.4 on ubuntu.

Mike


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