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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 parse_reactions(self):
 """Yield tuples of reaction ID and reactions defined in the model"""


        # Parse reactions defined in the main model file
        if 'reactions' in self._model:
            for reaction in parse_reaction_list(
                    self._context, self._model['reactions'],
                    self.default_compartment):
                yield reaction