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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 copy(self):
 """Return copy of model"""


        model = self.__class__(self._database)
        model._limits_lower = dict(self._limits_lower)
        model._limits_upper = dict(self._limits_upper)
        model._reaction_set = set(self._reaction_set)
        model._compound_set = set(self._compound_set)
        return model