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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 enter_frame(self, frame):
 """Remember all undeclared identifiers."""

        CodeGenerator.enter_frame(self, frame)
        for _, (action, param) in iteritems(frame.symbols.loads):
            if action == 'resolve':
                self.undeclared_identifiers.add(param)