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POVirtual classes: doing it right?
 

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  1. POVirtual classes: doing it right?
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    <p>I have been reading documentation describing class inheritance, abstract base classes and even python interfaces. But nothing seams to be exactly what I want. Namely, a simple way of building virtual classes. When the virtual class gets called, I would like it to instantiate some more specific class based on what the parameters it is given and hand that back the calling function. For now I have a summary way of rerouting calls to the virtual class down to the underlying class.</p> <p>The idea is the following:</p> <pre><code>class Shape: def __init__(self, description): if description == "It's flat": self.underlying_class = Line(description) elif description == "It's spiky": self.underlying_class = Triangle(description) elif description == "It's big": self.underlying_class = Rectangle(description) def number_of_edges(self, parameters): return self.underlying_class(parameters) class Line: def __init__(self, description): self.desc = description def number_of_edges(self, parameters): return 1 class Triangle: def __init__(self, description): self.desc = description def number_of_edges(self, parameters): return 3 class Rectangle: def __init__(self, description): self.desc = description def number_of_edges(self, parameters): return 4 shape_dont_know_what_it_is = Shape("It's big") shape_dont_know_what_it_is.number_of_edges(parameters) </code></pre> <p>My rerouting is far from optimal, as only calls to the number_of_edges() function get passed on. Adding something like this to Shape doesn't seam to do the trick either:</p> <pre><code>def __getattr__(self, *args): return underlying_class.__getattr__(*args) </code></pre> <p>What I am doing wrong ? Is the whole idea badly implemented ? Any help greatly appreciated.</p>
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    1. USmartineau
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    1. CO`__getattr__` works only for new-style classes. This means your classes have to be subclasses of `object`.
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      1. USGeorg Schölly
 

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