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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 Validate(self):
 """The filter exists, and has valid filter and hint expressions."""

    if self.type not in filters.Filter.classes:
      raise DefinitionError("Undefined filter type %s" % self.type)
    self._filter.Validate(self.expression)
    Validate(self.hint, "Filter has invalid hint")