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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 update_headers(self, headers: Optional[LooseHeaders]) -> None: """Update request headers."""

        self.headers = CIMultiDict()  # type: CIMultiDict[str]

        # add host
        netloc = cast(str, self.url.raw_host)
        if helpers.is_ipv6_address(netloc):
            netloc = '[{}]'.format(netloc)
        if not self.url.is_default_port():
            netloc += ':' + str(self.url.port)
        self.headers[hdrs.HOST] = netloc

        if headers:
            if isinstance(headers, (dict, MultiDictProxy, MultiDict)):
                headers = headers.items()  # type: ignore

            for key, value in headers:
                # A special case for Host header
                if key.lower() == 'host':
                    self.headers[key] = value
                else:
                    self.headers.add(key, value)