[Python-Dev] Indexing builtin sequences with objects which supply __int__

Tim Peters tim.one@comcast.net
Sun, 23 Jun 2002 14:45:30 -0400

[Todd Miller, wants to use rank-0 arrays as regular old indices]

> Here's a sick idea:  given Python 2.2, you *could* make the type
> of a rank-0 array a subclass of Python's int type

> Right now, numarray is a subclass of object for Python-2.2 in order to
> get properties in order to emulate some of Numeric's attributes. I'm
> wondering what I'd loose from object in order to pick up int's indexing.

All types in 2.2 inherit from object, including int.

>>> class IntWithA(int):
...     def seta(self, value):
...         self._a = value
...     def geta(self):
...         return self._a * 2
...     a = property(geta, seta)
>>> i = IntWithA(42)
>>> i
>>> i.a = 333
>>> i.a
>>> range(50)[i]

So, e.g., adding arbitrary properties should be a crawl in the park.

>  I'm also wondering how to make a rank-0 Float array fail as an index.

Quit while you're ahead <wink>.  The obvious idea is to make a
Rank0FloatArray type which is not a subclass of int.