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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 charset(self):
 """The charset from the content type."""

        header = self.environ.get('CONTENT_TYPE')
        if header:
            ct, options = parse_options_header(header)
            charset = options.get('charset')
            if charset:
                if is_known_charset(charset):
                    return charset
                return self.unknown_charset(charset)
        return self.default_charset