[Numpy-discussion] Please help with subclassing numpy.ndarray
Mon Feb 5 11:25:00 CST 2007
On Monday 05 February 2007 11:32:22 Jeremy Conlin wrote:
> Thanks for clarifying that. I didn't understand what the
> __array_finalize__ did.
That means I should clarify some points on the wiki, then.
A good exercise is to put some temporary comments in your code in __new__ and
__array_finalize__, to show when these methods are called and how (that's how
Thinking about it, the example you gave can't work. Your __new__ method
returns H, viz, a pure ndarray. There won't be any call to __array_finalize__
in that case, which is not what you want. Force the call by accessing a view
of your array:
def __new__(self, iniarray, inibin):
(H,edges) = N.histogramdd(iniarray,inibin)
self._defedges = edges
Now, you do return a 'myhistog' class, not a pure 'ndarray', and
__array_finalize__ is called.
def __array_finalize__(self, obj):
print "__array_finalize__ got %s as %s" % (obj, type(obj))
if not hasattr(self, 'edges'):
self.edges = self._defedges
myhistog._defedges = None
Note the last line: you reset the class default to None (if this is what you
want). Otherwise, new 'myhistog' objects wil inherit the previous edges.
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