Re: [Numpy-discussion] Help on subclassing numpy.ma: __array_wrap__
Kevin,
Sorry for the delayed answer.
(a) Is MA intended to be subclassed?
Yes, that's actually the reason why the class was rewritten, to
simplify subclassing. As Josef suggested, you can check the
scikits.timeseries package that makes an extensive use of MaskedArray
as baseclass.
(b) If so, perhaps I'm missing something to make this work. Any
pointers will be appreciated.
As you've run a debugger on your sources, you must have noticed the
calls to MaskedArray._update_from. In your case, the simplest is to
define DTMA._update_from as such:
_
def _update_from(self, obj):
ma.MaskedArray._update_from(self, obj)
self._attr = getattr(obj, '_attr', {'EmptyDict':[]})
_
Now, because MaskedArray.__array_wrap__() itself calls _update_from,
you don't actually need a specific DTMA.__array_wrap__ (unless you
have some specific operations to perform, but it doesn't seem to be
the case).
Now for a word of explanation:
__array_wrap__ is intended to transform the output of a numpy function
to an object of your class. When we use the numpy.ma functions, we
don't need that, we just need to retrieve some of the attributes of
the initial MA. That's why _update_from was introduced.
Of course, I'm to blame not to have make that aspect explicit in the
doc. I gonna try to correct that.
In any case, let me know how it goes.
P.
On Mar 1, 2009, at 10:37 AM, Kevin Dunn wrote:
Hi everyone,
I'm subclassing Numpy's MaskedArray to create a data class that
handles missing data, but adds some extra info I need to carrry
around. However I've been having problems keeping this extra info
attached to the subclass instances after performing operations on
them.
The bare-bones script that I've copied here shows the basic issue:
http://pastebin.com/f69b979b8
There are 2 classes: one where I am able to subclass numpy (with
help from the great description at http://www.scipy.org/Subclasses),
and the other where I subclass numpy.ma, using the same ideas again.
When stepping through the code in a debugger, lines 76 to 96, I can
see that the numpy subclass, called DT, calls DT.__array_wrap__()
after it completes unary and binary operations. But the numpy.ma
subclass, called DTMA, does not seem to call DTMA.__array_wrap__(),
especially line 111.
Just to test this idea, I overrode the __mul__ function in my DTMA
subclass to call DTMA.__array_wrap__() and it returns my extra
attributes, in the same way that Numpy did.
My questions are:
(b) If so, perhaps I'm missing something to make this work. Any
pointers will be appreciated.
So far it seems the only way for me to sub-class numpy.ma is to
override all numpy.ma functions of interest for my class and add a
DTMA.__array_wrap() call to the end of them. Hopefully there is an
easier way.
Related to this question, was there are particular outcome from this
archived discussion (I only joined the list recently):
http://article.gmane.org/gmane.comp.python.numeric.general/24315
because that dictionary object would be exactly what I'm after here.
Thanks,
Kevin
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[Numpy-discussion] Help on subclassing numpy.ma: __array_wrap__
Hi everyone, I'm subclassing Numpy's MaskedArray to create a data class that handles missing data, but adds some extra info I need to carrry around. However I've been having problems keeping this extra info attached to the subclass instances after performing operations on them. The bare-bones script that I've copied here shows the basic issue: http://pastebin.com/f69b979b8 There are 2 classes: one where I am able to subclass numpy (with help from the great description at http://www.scipy.org/Subclasses), and the other where I subclass numpy.ma, using the same ideas again. When stepping through the code in a debugger, lines 76 to 96, I can see that the numpy subclass, called DT, calls DT.__array_wrap__() after it completes unary and binary operations. But the numpy.ma subclass, called DTMA, does not seem to call DTMA.__array_wrap__(), especially line 111. Just to test this idea, I overrode the __mul__ function in my DTMA subclass to call DTMA.__array_wrap__() and it returns my extra attributes, in the same way that Numpy did. My questions are: (a) Is MA intended to be subclassed? (b) If so, perhaps I'm missing something to make this work. Any pointers will be appreciated. So far it seems the only way for me to sub-class numpy.ma is to override all numpy.ma functions of interest for my class and add a DTMA.__array_wrap() call to the end of them. Hopefully there is an easier way. Related to this question, was there are particular outcome from this archived discussion (I only joined the list recently): http://article.gmane.org/gmane.comp.python.numeric.general/24315 because that dictionary object would be exactly what I'm after here. Thanks, Kevin ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Help on subclassing numpy.ma: __array_wrap__
On Sun, Mar 1, 2009 at 10:37 AM, Kevin Dunn kgd...@gmail.com wrote: Hi everyone, I'm subclassing Numpy's MaskedArray to create a data class that handles missing data, but adds some extra info I need to carrry around. However I've been having problems keeping this extra info attached to the subclass instances after performing operations on them. The bare-bones script that I've copied here shows the basic issue: http://pastebin.com/f69b979b8 There are 2 classes: one where I am able to subclass numpy (with help from the great description at http://www.scipy.org/Subclasses), and the other where I subclass numpy.ma, using the same ideas again. When stepping through the code in a debugger, lines 76 to 96, I can see that the numpy subclass, called DT, calls DT.__array_wrap__() after it completes unary and binary operations. But the numpy.ma subclass, called DTMA, does not seem to call DTMA.__array_wrap__(), especially line 111. Just to test this idea, I overrode the __mul__ function in my DTMA subclass to call DTMA.__array_wrap__() and it returns my extra attributes, in the same way that Numpy did. My questions are: (a) Is MA intended to be subclassed? (b) If so, perhaps I'm missing something to make this work. Any pointers will be appreciated. So far it seems the only way for me to sub-class numpy.ma is to override all numpy.ma functions of interest for my class and add a DTMA.__array_wrap() call to the end of them. Hopefully there is an easier way. Related to this question, was there are particular outcome from this archived discussion (I only joined the list recently): http://article.gmane.org/gmane.comp.python.numeric.general/24315 because that dictionary object would be exactly what I'm after here. Thanks, Kevin timeseries in the scikits are subclassing MaskedArray and might provide some examples http://scipy.org/scipy/scikits/browser/trunk/timeseries/scikits/timeseries/tseries.py#L446 Josef ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
