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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 _id(self):
 """Handle identifiers and reserverd keywords."""

        result = ''
        while self.char is not None and (self.char.isalnum() or self.char == '_'):
            result += self.char
            self.advance()

        token = RESERVED_KEYWORDS.get(result, Token(Nature.ID, result))
        return token