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POobject oriented programming basics: inheritance & shadowing (Python)
 

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    <p>Level: Beginner</p> <p>I'm doing my first steps in Object Oriented programming. The code is aimed at showing how methods are passed up the chain. So when i call <code>UG.say(person, 'but i like')</code> the method <code>say</code> is instructed to call class <code>MITPerson</code>. Given that <code>MITPerson</code> does not contain a <code>say</code> method it will pass it up to class <code>Person</code>. I think there is nothing wrong with the code as it is part of a lecture (see source below). I think it is me who is omitting to define something when i run the code. Not sure what though. I think that the <code>UG instance</code> the error message is looking for as first argument is refering to <code>self</code> but that, in principle, doesn't need to be provided, correct? Any hints?</p> <pre><code>class Person(object): def __init__(self, family_name, first_name): self.family_name = family_name self.first_name = first_name def familyName(self): return self.family_name def firstName(self): return self.first_name def say(self,toWhom,something): return self.first_name + ' ' + self.family_name + ' says to ' + toWhom.firstName() + ' ' + toWhom.familyName() + ': ' + something class MITPerson(Person): def __init__(self, familyName, firstName): Person.__init__(self, familyName, firstName) class UG(MITPerson): def __init__(self, familyName, firstName): MITPerson.__init__(self, familyName, firstName) self.year = None def say(self,toWhom,something): return MITPerson.say(self,toWhom,'Excuse me, but ' + something) &gt;&gt;&gt; person = Person('Jon', 'Doe') &gt;&gt;&gt; person_mit = MITPerson('Quin', 'Eil') &gt;&gt;&gt; ug = UG('Dylan', 'Bob') &gt;&gt;&gt; UG.say(person, 'but i like') UG.say(person, 'bla') **EDIT (for completeness)**: it should say UG.say(person, 'but i like') #the 'bla' creeped in from a previous test TypeError: unbound method say() must be called with UG instance as first argument (got Person instance instead) </code></pre> <p>source: MIT OpenCourseWare <a href="http://ocw.mit.edu" rel="nofollow">http://ocw.mit.edu</a> Introduction to Computer Science and Programming Fall 2008</p>
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