Overloading "if object" unary operator

[Fredrik Lundh]

Sarcastic Zombie wrote:

> If I have a class
> 
> class A:
>     __init__(id)
>         self.id = id
> 
> is there any way to overload the 'if' unary usage to detect if a
> variable has a value?

http://effbot.org/pyref/__nonzero__

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