testing for valid reference: obj vs. None!=obs vs. obj is not None

[alf]

alf wrote:
> Hi,
> 
> I have a reference to certain objects. What is the most pythonic way to 
> test for valid reference:
> 
>     if obj:
> 
>     if None!=obs:
> 
>     if obj is not None:
> 
thx for all answers - now "if obj is not None:" in an obvious choice ...