class inheritance

JLundell jlundell at pobox.com
Sat Mar 13 18:03:36 CET 2010


I've got a subclass of fractions.Fraction called Value; it's a mostly
trivial class, except that it overrides __eq__ to mean 'nearly equal'.
However, since Fraction's operations result in a Fraction, not a
Value, I end up with stuff like this:

x = Value(1) + Value(2)

where x is now a Fraction, not a Value, and x == y uses
Fraction.__eq__ rather than Value.__eq__.

This appears to be standard Python behavior (int does the same thing).
I've worked around it by overriding __add__, etc, with functions that
invoke Fraction but coerce the result. But that's tedious; there are a
lot of methods to override.

So I'm wondering: is there a more efficient way to accomplish what I'm
after?



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