官方文档：https://docs.python.org/3.5/library/http.html
偷个懒，截图如下：
即，http客户端编程一般用urllib.request库（主要用于“在这复杂的世界里打开各种url”，包括：authentication、redirections、cookies and more.）。
1. urllib.request—— Extensible library for opening URLs
使用手册，结合代码写的很详细：HOW TO Fetch Internet Resources Using The urllib Package
该模块提供的函数：
urllib.request.urlopen(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)
urllib.request.install_opener(opener)
urllib.request.build_opener([handler, ...])
urllib.request.pathname2url(path)
urllib.request.url2pathname(path)
urllib.request.getproxies()
该模块提供的类：
class urllib.request.Request(url, data=None, headers={}, origin_req_host=None, unverifiable=False, method=None)
class urllib.request.OpenerDirector
class urllib.request.BaseHandler
class urllib.request.HTTPDefaultErrorHandler
class urllib.request.HTTPRedirectHandler
class urllib.request.HTTPCookieProcessor(cookiejar=None)
class urllib.request.ProxyHandler(proxies=None)
class urllib.request.HTTPPasswordMgr
还有很多，不一一列出了。。。
1.2 Request对象
下面的方法是Request提供的公共接口，所以它们可以被子类重写。同时，也提供了一些客户端可以查阅解析的请求的公共属性。
Request.full_url Request.type Request.host Request.origin_req_host #不包含端口号
Request.selector Request.data Request.unverifiable Request.method
Request.get_method() Request.add_header(key, val) Request.add_unredirected_header(key, header) Request.has_header(header) Request.remove_header(header)
Request.get_full_url() Request.set_proxy(host, type) Request.get_header(header_name, default=None) Request.header_items()
1.3 OpenerDirector Objects
有以下方法：
OpenerDirector.add_handler(handler)
OpenerDirector.open(url, data=None[, timeout])
OpenerDirector.error(proto, *args)
1.4 BaseHandler Objects
1.5 HTTPRedirectHandler Objects
1.6 HTTPCookieProcessor Objects
它只有一个属性：HTTPCookieProcessor.cookiejar ，所有的cookies都保存在http.cookiejar.CookeiJar中。
1.x 还有太多类，需要用时直接查看官方文档吧。。
EXamples
打开url读取数据：
>>> import urllib.request
>>> with urllib.request.urlopen('http://www.python.org/') as f:
... print(f.read(300))
...
b'<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html
xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>Python Programming '
注意：urlopen返回一个bytes object（字节对象）。
>>> with urllib.request.urlopen('http://www.python.org/') as f:
... print(f.read(100).decode('utf-8'))
...
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtm
向CGI的stdin发送数据流：
>>> import urllib.request
>>> req = urllib.request.Request(url='https://localhost/cgi-bin/test.cgi',
... data=b'This data is passed to stdin of the CGI')
>>> with urllib.request.urlopen(req) as f:
... print(f.read().decode('utf-8'))
...
Got Data: "This data is passed to stdin of the CGI"
CGI的另一端通过stdin接收数据：
#!/usr/bin/env python
import sys
data = sys.stdin.read()
print('Content-type: text/plain
Got Data: "%s"' % data)
Use of Basic HTTP Authentication:
import urllib.request
# Create an OpenerDirector with support for Basic HTTP Authentication...
auth_handler = urllib.request.HTTPBasicAuthHandler()
auth_handler.add_password(realm='PDQ Application',
uri='https://mahler:8092/site-updates.py',
user='klem',
passwd='kadidd!ehopper')
opener = urllib.request.build_opener(auth_handler)
# ...and install it globally so it can be used with urlopen.
urllib.request.install_opener(opener)
urllib.request.urlopen('http://www.example.com/login.html')
添加HTTP头部：
import urllib.request
req = urllib.request.Request('http://www.example.com/')
req.add_header('Referer', 'http://www.python.org/')
# Customize the default User-Agent header value:
req.add_header('User-Agent', 'urllib-example/0.1 (Contact: . . .)')
r = urllib.request.urlopen(req)
OpenerDirector automatically adds a User-Agent header to every Request. To change this:
import urllib.request
opener = urllib.request.build_opener()
opener.addheaders = [('User-agent', 'Mozilla/5.0')]
opener.open('http://www.example.com/')
Also, remember that a few standard headers (Content-Length, Content-Type and Host) are added when the Request is passed to urlopen() (or OpenerDirector.open()).
GET：
>>> import urllib.request
>>> import urllib.parse
>>> params = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
>>> url = "http://www.musi-cal.com/cgi-bin/query?%s" % params
>>> with urllib.request.urlopen(url) as f:
... print(f.read().decode('utf-8'))
POST：
>>> import urllib.request
>>> import urllib.parse
>>> data = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
>>> data = data.encode('ascii')
>>> with urllib.request.urlopen("http://requestb.in/xrbl82xr", data) as f:
... print(f.read().decode('utf-8'))
The following example uses an explicitly specified HTTP proxy, overriding environment settings:
>>> import urllib.request
>>> proxies = {'http': 'http://proxy.example.com:8080/'}
>>> opener = urllib.request.FancyURLopener(proxies)
>>> with opener.open("http://www.python.org") as f:
... f.read().decode('utf-8'
The following example uses no proxies at all, overriding environment settings：
>>> import urllib.request
>>> opener = urllib.request.FancyURLopener({})
>>> with opener.open("http://www.python.org/") as f:
... f.read().decode('utf-8')