[Python-Dev] subclassing builtin data structures (original) (raw)

Alexander Belopolsky alexander.belopolsky at gmail.com
Sat Feb 14 21:47:28 CET 2015

On Sat, Feb 14, 2015 at 2:36 PM, Georg Brandl <g.brandl at gmx.net> wrote:

> In the case of int, there is a good reason for this behavior - bool. In python, > we want True + True == 2. In numpy, where binary operations preserve > subclasses, you have > >>>> import numpy >>>> numpy.bool(1) + numpy.bool(1) > True

I don't think numpy.bool subclasses some class like numpy.int.

And numpy.bool_ subclasses don't preserve type in addition:

import numpy class Bool(numpy.bool): ... pass ... numpy.bool.mro() [<class 'numpy.bool_'>, <class 'numpy.generic'>, <class 'object'>] Bool(1) + Bool(1) True type() <class 'numpy.bool_'>

So there goes my theory. :-)

I think all these examples just highlight the need for a clear guidance when self.class() can be called in base classes to construct instances of derived classes.

Apparently numpy has it both ways. One way for scalars (see above) and the other for arrays:

class Array(numpy.ndarray): ... pass ... a = Array(1) a[0] = 1 a+a Array([ 2.]) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20150214/de330263/attachment.html>

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