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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 one_of(self, chset: str) -> str: """Parse one character form the specified set. Args: chset: string of characters to try as alternatives. Returns: The character that was actually matched. Raises: UnexpectedInput: If the next character is not in `chset`. """

        res = self.peek()
        if res in chset:
            self.offset += 1
            return res
        raise UnexpectedInput(self, "one of " + chset)