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

[Dag Sverre Seljebotn]

Dag Sverre Seljebotn wrote:

> [1] Like just checking if you're within an if-test where the local 
> variable was checked to not be None + only the first attribute lookup on 
> a local variable in the same block needs a check, because an exception 
> drops you out of it. These two rules gets you a long way.
> 

(All this Cython only but keeping the thread intact...)

Sorry: And any assignments to a local variable will reset the state to 
now known, that must be dealt with too. I'm not saying that this is a 
magic bullet, just that code like

cdef MyClass x = ...
if x is not None:
     block without assignment to x

could be a convenient way to declare intent and generate efficient code 
(kind of like how if-statements are currently translated to switch 
statements under certain strict conditions)

(Hmm, in that view, a special type like cython.nonnone(MyClass) is 
perhaps not needed, an "assert x is not None" after every assignment to 
x could fill the same role)

-- 
Dag Sverre