[Numpy-discussion] use of concatenate with subclass of ndarray

Bryce Hendrix bhendrix@enthought....
Wed Mar 28 11:42:52 CDT 2007


Thanks Pierre, works like a charm. One question though, how is defining 
a class attribute in __new__ any more thread-safe?

Bryce

Pierre GM wrote:
> On Tuesday 27 March 2007 20:08:04 Bryce Hendrix wrote:
>   
>> We have a class which is a subclass of ndarray which defines
>> __array_finalize__ to add an attribute. The class looks something like
>> this:
>>     
>
> Ahah, we ran into this problem a few months ago:
> You should not initialize your "units" attribute in the __new__ method, as 
> it's not thread-safe first, but more important as you will lose it if you try 
> to get a view of your new object (because in that case, __new__ is not 
> called).
> Instead, try something like that:
>
> def __array_finalize__(self, obj):
> 	self.units = getattr(obj, 'units', yourdefaultunit)
>
> where your defaultunit is the value you would use in __new__. True, 
> yourdefaultunit may change, and even be lost if there's a break between 
> __new__ and __array_finalize__, but that should work. Lemme know.
>
> Note that things are always tricky w/ concatenate: when you concatenate your 
> UnitArray, you should have a UnitArray, OK. But if you mix UnitArray and 
> ndarray ? What should take precedence ?
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