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

[Pierre GM]

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 ?