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默认情况下，HOST标头不会添加到请求中requests。如果没有明确添加，则将决策委托给底层http模块。请参阅以下部分http/client.py：（如果在then is'Host'中明确提供了标题）requests.getskip_hostTrue if self._http_vsn == 11: # Issue some standard headers for better HTTP/1.1 compliance if not skip_host: # this header is issued *only* for HTTP/1.1 # connections. more specifically, this means it is # only issued when the client uses the new # HTTPConnection() class. backwards-compat clients # will be using HTTP/1.0 and those clients may be # issuing this header themselves. we should NOT issue # it twice; some web servers (such as Apache) barf # when they see two Host: headers # If we need a non-standard port,include it in the # header. If the request is going through a proxy, # but the host of the actual URL, not the host of the # proxy. netloc = '' if url.startswith('http'): nil, netloc, nil, nil, nil = urlsplit(url) if netloc: try: netloc_enc = netloc.encode("ascii") except UnicodeEncodeError: netloc_enc = netloc.encode("idna") self.putheader('Host', netloc_enc) else: if self._tunnel_host: host = self._tunnel_host port = self._tunnel_port else: host = self.host port = self.port try: host_enc = host.encode("ascii") except UnicodeEncodeError: host_enc = host.encode("idna") # As per RFC 273, IPv6 address should be wrapped with [] # when used as Host header if host.find(':') >= 0: host_enc = b'[' + host_enc + b']' if port == self.default_port: self.putheader('Host', host_enc) else: host_enc = host_enc.decode("ascii") self.putheader('Host', "%s:%s" % (host_enc, port)) 因此，'Host'在检查requests发送到服务器的标头时，我们看不到标头。如果我们向http://httpbin/get发送请求并打印响应，我们可以看到Host标头确实已发送。import requestsresponse = requests.get("http://httpbin.org/get")print('Response from httpbin/get')print(response.json())print()print('response.request.headers')print(response.request.headers)输出Response from httpbin/get{'args': {}, 'headers': {'Accept': '*/*', 'Accept-Encoding': 'gzip, deflate', 'Host': 'httpbin.org', 'User-Agent': 'python-requests/2.20.0'}, 'origin': 'XXXXXX', 'url': 'https://httpbin.org/get'}response.request.headers{'User-Agent': 'python-requests/2.20.0', 'Accept-Encoding': 'gzip, deflate', 'Accept': '*/*', 'Connection': 'keep-alive'}