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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 match_regex(self, regex: Pattern, required: bool = False, meaning: str = "") -> str: """Parse input based on a regular expression . Args: regex: Compiled regular expression object. required: Should the exception be raised on unexpected input? meaning: Meaning of `regex` (for use in error messages). Raises: UnexpectedInput: If no syntactically correct keyword is found. """

        mo = regex.match(self.input, self.offset)
        if mo:
            self.offset = mo.end()
            return mo.group()
        if required:
            raise UnexpectedInput(self, meaning)