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POIssue with python class hierarchy
 

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    <p>I have a class hierarchy:</p> <pre><code>class ParentClass: def do_something(self): pass # child classes have their own implementation of this class ChildClass1(ParentClass): def do_something(self): &lt;implementation here&gt; class ChildClass2(ParentClass): def do_something(self, argument_x): &lt;implementation here&gt; class ChildClass3(ParentClass): def do_something(self, argument_y): &lt;implementation here&gt; </code></pre> <p>There are two problems here:</p> <ul> <li>method do_something() has different interfaces in subclasses: it accepts an argument in child classes 2 and 3, but has no argument in child class 1</li> <li>the arguments of do_something() have different names to emphasize that they have different meanings in child classes 2 and 3. This will become clearer below, from the usage example</li> </ul> <p>This is how the classes are used:</p> <p>There is a factory class that returns instances:</p> <pre><code>class ChildFactory: def get_child(self, argument): if argument == '1': return ChildClass1() elif argument == '2': return ChildClass2() elif argument == '3': return ChildClass3() </code></pre> <p>later in code:</p> <pre><code>... # pseudocode, not python child_type = ? # can have values '1', '2' or '3' at this moment var1 = 1 var2 = 'xxx' # var1 and var2 have different types, just to emphasize the difference in their # meaning when being passed as arguments to do_something() # this was mentioned above (the second problem) child = ChildFactory.get_child(child_type) if child is an instance of ChildClass1, child.do_something() is called if child is an instance of ChildClass2, child.do_something(var1) is called if child is an instance of ChildClass3, child.do_something(var2) is called # end of pseudocode </code></pre> <p>Questions:</p> <ol> <li>Are the two problems mentioned above a sign of a bad design? If so, what's the correct way to design the hierarchy?</li> <li>How to write the pseudocode snippet uniformly in python? The main concern is to avoid using a huge if/else statement for each particular case, because it will double the if/else statement from ChildFactory.get_child()</li> </ol>
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