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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 key_rule(self, regex, verifier):
 """Add a rule with a pattern that should apply to all keys. Any key not explicitly listed in an add_required or add_optional rule must match ONE OF the rules given in a call to key_rule(). So these rules are all OR'ed together. In this case you should pass a raw string specifying a regex that is used to determine if the rule is used to check a given key. Args: regex (str):
 The regular expression used to match the rule or None if this should apply to all verifier (Verifier):
 The verification rule """


        if regex is not None:
            regex = re.compile(regex)

        self._additional_key_rules.append((regex, verifier))