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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 _add_missing_schema_attributes(self):
        '''
        Adds any missed schema attributes to the _attributes list

        The attributes can be class attributes and they won't be
        included in the _attributes list automatically
        '''
        for attr in [attr for attr in dir(self) if not attr.startswith('__')]:
            attr_val = getattr(self, attr)
            if isinstance(getattr(self, attr), SchemaItem) and \
               attr not in self._attributes:

                self._attributes.append(attr)