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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 save(self):
 """ persist the fields in this object into the db, this will update if _id is set, otherwise it will insert see also -- .insert(), .update() """

        ret = False

        # we will only use the primary key if it hasn't been modified
        pk = None
        if self.schema.pk.name not in self.modified_fields:
            pk = self.pk

        if pk:
            ret = self.update()
        else:
            ret = self.insert()

        return ret