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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 re_keys(self, pattern):
 """Find keys matching `pattern`. :param pattern: Regular expression :return: Matching keys or empty list :rtype: list """

        if not pattern.endswith("$"):
            pattern += "$"
        expr = re.compile(pattern)
        return list(filter(expr.match, self.keys()))