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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 allowed_classes(self):
 """Iterate over the allowed classes for this slot. The Python equivalent of the CLIPS slot-allowed-classes function. """

        data = clips.data.DataObject(self._env)

        lib.EnvSlotAllowedClasses(
            self._env, self._cls, self._name, data.byref)

        if isinstance(data.value, list):
            for klass in classes(self._env, data.value):
                yield klass