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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 sources(self):
 """A tuple containing the names of the Class sources for this Slot. The Python equivalent of the CLIPS slot-sources function. """

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

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

        return tuple(data.value) if isinstance(data.value, list) else ()