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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _get_argname_value(self, argname):
        '''
        Return the argname value looking up on all possible attributes
        '''
        # Let's see if there's a private function to get the value
        argvalue = getattr(self, '__get_{0}__'.format(argname), None)
        if argvalue is not None and callable(argvalue):
            argvalue = argvalue()
        if argvalue is None:
            # Let's see if the value is defined as a public class variable
            argvalue = getattr(self, argname, None)
        if argvalue is None:
            # Let's see if it's defined as a private class variable
            argvalue = getattr(self, '__{0}__'.format(argname), None)
        if argvalue is None:
            # Let's look for it in the extra dictionary
            argvalue = self.extra.get(argname, None)
        return argvalue