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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 by_type(self, identifier_class):
 """ returns all unique instances of a type of identifier :param identifier_class: the class to match identifier with :returns: a tuple """

        myidentifiers = set()
        for identifier in self.source_identifiers.values():
            if (isinstance(identifier, identifier_class)):
                myidentifiers.update([identifier])
        return set(myidentifiers)