[Numpy-discussion] subclassing float64 (and friends)
oliphant at ee.byu.edu
Wed Jan 3 16:53:43 EST 2007
eric jones wrote:
>I am playing around with sub-classing the new-fangled float64 objects
>and friends. I really like the new ndarray subclassing features
>(__array_finalize__, etc.), and was exploring whether or not the scalars
>worked the same way. I've stubbed my toe right out of the blocks
>though. I can sub-class from standard python floats just fine, but when
>I try to do the same from float64, I get a traceback. (examples below)
>Anyone have ideas on how to do this correctly?
Unfortunately, the array scalars were not originally designed to be
sub-classed. I believe I later set the flag saying they "could be"
sub-classable. However, I did not alter the tp_new code to actually use
the type information passed in as the first argument to actually create
an instance of the sub-class --- effectively making the array scalars
Thus, the _arrtype_new code would need to be changed in
scalartypes.inc.src to fix this. Notice that in Python the float_new
command does a special check for when a sub-type is requested and calls
float_subtype_new which creates a regular float and then copies the data
over to the sub-type.
This special-check is not done in the tp_new function
(<name>_arrtype_new) and so float64.__new__ will *always* return the
array scalars are still not sub-classable (except for the void
scalar). This could be changed, and needs to happen before
sub-classing of array scalars will work.
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