[Cython] a question about Shadow.py

[Robert Bradshaw]

On Apr 24, 2009, at 3:07 PM, Lisandro Dalcin wrote:

> On Fri, Apr 24, 2009 at 6:41 PM, Robert Bradshaw
> <robertwb at math.washington.edu> wrote:
>> On Apr 24, 2009, at 1:48 PM, Lisandro Dalcin wrote:
>>
>>> On Fri, Apr 24, 2009 at 4:27 PM, Robert Bradshaw
>>> <robertwb at math.washington.edu> wrote:
>>>> On Apr 24, 2009, at 8:17 AM, Lisandro Dalcin wrote:
>>>
>>> Of course, then if  @cython.cdivision(True) is used, the code in
>>> Shadow should emit a warning, right?
>>
>> No idea how one would do this...
>>
>
> Perhaps something like this

Sorry, for some reason I was thinking about  
@cython.cdivision_warnings which would be really hard to emulate in  
pure Python...

> (sorry if identation is wrong, still
> missing native support for fixed-width fonts when composing mails in
> Gmail)
>
> # In Shadow.py
> class cdivision:
>   def __init__(self, value):
>        assert type(value) is bool
>        self.value = value
>   def __call__(self, function):
>        if self.value: warn("C division semantics cannot work on  
> Python code")
>        return function

C has undefined division semantics, so Python semantics are fine with  
cython.cdivision(True) (though I have yet to run into that in  
practice). However, almost every compiler directive can't be emulated  
in pure Python mode (e.g. we don't truncate integers), so I am of the  
opinion that they should just be vacuous and ignored rather than all  
raise warnings.

- Robert