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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 get_foreign_key(self, name):
 """ Returns the foreign key constraint with the given name. :param name: The constraint name :type name: str :rtype: ForeignKeyConstraint """

        name = self._normalize_identifier(name)

        if not self.has_foreign_key(name):
            raise ForeignKeyDoesNotExist(name, self._name)

        return self._fk_constraints[name]