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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 validatePrivate(self, field, value) : """validate a private field value"""

        if field not in self.arangoPrivates :
            raise ValueError("%s is not a private field of collection %s" % (field, self))

        if field in self._fields :
            self._fields[field].validate(value)
        return True