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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 find(self, header):
 """Return the index of the header in the set or return -1 if not found. :param header: the header to be looked up. """

        header = header.lower()
        for idx, item in enumerate(self._headers):
            if item.lower() == header:
                return idx
        return -1