[Cython] [Pyrex] Proposed change to behaviour of "not None"

[Dag Sverre Seljebotn]

Stefan Behnel wrote:

> It would be nice if this could be solved by better flow analysis, but I doubt
> that it can be achieved with reasonable effort.

I disagree, I've been thinking about it and I think I could make 
something covering a lot of cases with a week or two full time. (Those 
are young and bold words of course but I'm just making a statement of my 
beliefs, not saying you have to share them :-) ).

Not that I have that now, it is just that I don't think two weeks should 
be considered an unreasonable effort for something like this.

Or perhaps it is unreasonable relative to the developer resources of 
Cython, but Cython is gaining user mass and that might very well change. 
So I'd like control flow analysis to remain the plan...

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Dag Sverre