>>> import requests
>>> res = requests.head("http://www.baidu.com/")
>>> req.head("https://www.baidu.com/").headers
{'Content-Encoding': 'gzip', 'Server': 'bfe/1.0.8.18', 'Last-Modified': 'Mon, 13 Jun 2016 02:50:08 GMT', 'Connection': 'Keep-Alive', 'Pragma': 'no-cache', 'Cache-Control': 'private, no-cache, no-store, proxy-revalidate, no-transform', 'Date': 'Fri, 13 Oct 2017 04:36:20 GMT', 'Content-Type': 'text/html'}
>>> res.ok
True
>>> res.content
''
# 但是會遇到一些問題, 比如, 服務器不支持 HEAD, 或者拒絕 HEAD.
# 如下情況就被拒絕
#
>>> res = req.head("https://www.douban.com/subject/1/")
>>> res
<Response [403]>
>>> res.ok
False
>>> res.content
''
>>> res.headers
{'Content-Encoding': 'gzip', 'Keep-Alive': 'timeout=30', 'Server': 'dae', 'Connection': 'keep-alive', 'Date': 'Fri, 13 Oct 2017 04:39:00 GMT', 'Content-Type': 'text/html'}

import urllib
>>> res = urllib.urlopen("http://127.0.0.1:8000/git.exe")
>>> res.url
'http://127.0.0.1:8000/git.exe'
>>> res.headers.headers
['Server: SimpleHTTP/0.6 Python/2.7.10\r\n', 'Date: Fri, 13 Oct 2017 06:06:37 GMT\r\n', 'Content-type: application/x-msdownload\r\n', 'Content-Length: 7569408\r\n', 'Last-Modified: Fri, 16 Dec 2016 07:09:32 GMT\r\n']
>>> len(r.read())
7569408
# urllib 只有在調用 read/readline/readlines 的時候才會從 web 服務器讀取數據.
# 源碼可以在 urllib/httplib 中找到. 
# urllib.py
def urlopen(url, ...):
 opener = FancyURLopener()
 return opener.open(url)
class FancyURLopener(URLopener).open():
 getattr(self, name)(url)
class URLopener.open_http():
 errcode, errmsg, headers = h.getreply()
 if(200 <= errcode < 300):
  return addinfourl(fp, headers, "http:" + url, errcode)
 else:
  if data is None:
   return self.http_error(url, fp, errcode, errmsg, headers)
  else:
   return self.http_error(url, fp, errcode, errmsg, headers, data)
class URLopener.http_error():
 return method(url, fp, errcode, errmsg, headers)
class FancyURLopener.http_error_default():
 return addinfourl(fp, headers, "http:" + url, errcode)
class addinfourl(addbase):
 # 代碼中并沒有對 fp 做任何操作,包括讀寫. 
class addbase.__init __():
 self.fp = fp
 self.read = self.fp.read
 self.readline = self.fp.readline
 if hasattr(self.fp, "readlines"): self.readlines = self.fp.readlines
  self.fileno = self.fp.fileno
 # ... ...

import socket
import ssl


_timeout = 10
socket.setdefaulttimeout(_timeout)

def get_header(host, port=80, uri="/", method="GET", user_ssl=False):
 # 這里可以再擴充一下, 支持 headers
 conn = None
 header = """%s %s HTTP/1.1\r\nHost: %s\r\nConnection: close\r\nUser-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36\r\n\r\n""" % (
  method, uri, host)
 if user_ssl:
  ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
  _socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  conn = ssl_context.wrap_socket(_socket, server_hostname=host)
  conn.connect((host, port))
  conn.send(header)
 else:
  conn = socket.create_connection((host, port), _timeout)
  conn.sendall(header)
 text = ""
 while True:
  if "\r\n\r\n" in text:
   break
  buff = conn.recv(10)
  text += buff
  # print buff
 conn.close()
 return text.split("\r\n\r\n")[0]

if __name__ == '__main__':
 print get_header("www.douban.com", uri="/subject/27076001/")
 print
 print get_header("www.douban.com", uri="/subject/27076001/", port=443, user_ssl=True)

➜ 76[14:48:20]zhipeng@zhipeng-MacBook ~/demo/python
�� $ python test_header.py
HTTP/1.1 301 Moved Permanently
Date: Fri, 13 Oct 2017 06:48:23 GMT
Content-Type: text/html
Content-Length: 178
Connection: close
Location: https://www.douban.com/subject/27076001/
Server: dae

HTTP/1.1 302 Moved Temporarily
Server: ADSSERVER/45863
Date: Fri, 13 Oct 2017 06:48:23 GMT
Content-Type: text/html
Transfer-Encoding: chunked
Connection: close
Location: https://sec.douban.com/b?r=https%3A%2F%2Fwww.douban.com%2Fsubject%2F27076001%2F
Strict-Transport-Security: max-age=15552000;
Set-Cookie: __ads_session=uY8l3pLW/AjCKJ8Y4wA=; domain=.douban.com; path=/
X-Powered-By-ADS: uni-jnads-1-02
➜ 77[14:48:23]zhipeng@zhipeng-MacBook ~/demo/python 
�� $