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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 check_verifier(self, verifier):
 """Checks that the verifier contains only safe characters and is no shorter than lower and no longer than upper. """

        lower, upper = self.verifier_length
        return (set(verifier) <= self.safe_characters and
                lower <= len(verifier) <= upper)