协程及其原理和应用

1.协程

 1 import gevent
 2 
 3 
 4 def foo():
 5     print('Running in foo')
 6     gevent.sleep(0)
 7     print('Explicit context switch to foo again')
 8 
 9 
10 def bar():
11     print('Explicit context to bar')
12     gevent.sleep(0)
13     print('Implicit context switch back to bar')
14 '''
15 遇到sleep就切换到下一个
16 '''
17 
18 gevent.joinall([
19     gevent.spawn(foo),
20     gevent.spawn(bar),
21 ])

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结果显示：如注释所写，遇到sleep就切换。

Running in foo
Explicit context to bar
Explicit context switch to foo again
Implicit context switch back to bar

2.协程原理

 1 def consumer(name):
 2     print("--->starting eating baozi...")
 3     while True:
 4         new_baozi = yield
 5         print("[%s] is eating baozi %s" % (name, new_baozi))
 6         # time.sleep(1)
 7 
 8 
 9 def producer():
10     r = con.__next__()
11     r = con2.__next__()
12     n = 0
13     while n < 5:
14         n += 1
15         con.send(n)
16         con2.send(n)
17         print("33[32;1m[producer]33[0m is making baozi %s" % n)
18 
19 
20 if __name__ == '__main__':
21     con = consumer("c1")
22     con2 = consumer("c2")
23     p = producer()

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上述的代码是之前所学到的吃包子。其中几点注意：

1.只有含有yield的函数才能有next方法。现在一般为next（conn）

2.执行next方法后函数才会运行（函数加括号不能启动函数），遇到yield后冻结，返回yield后的值给调用next的对象。

3.send也有next的效果，但是是将自己值送给yield前面的变量。但是不能先手send。send不能启动函数

结果显示：

 1 --->starting eating baozi...
 2 --->starting eating baozi...
 3 [c1] is eating baozi 1
 4 [c2] is eating baozi 1
 5 [producer] is making baozi 1
 6 [c1] is eating baozi 2
 7 [c2] is eating baozi 2
 8 [producer] is making baozi 2
 9 [c1] is eating baozi 3
10 [c2] is eating baozi 3
11 [producer] is making baozi 3
12 [c1] is eating baozi 4
13 [c2] is eating baozi 4
14 [producer] is making baozi 4
15 [c1] is eating baozi 5
16 [c2] is eating baozi 5
17 [producer] is making baozi 5

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3.爬虫

 1 from gevent import monkey
 2 import time
 3 
 4 monkey.patch_all()   # 监听IO口的程序 大量节约时间
 5 import gevent
 6 from  urllib.request import urlopen
 7 
 8 
 9 def f(url):
10     print('GET: %s' % url)
11     resp = urlopen(url)
12     data = resp.read()
13     print('%d bytes received from %s.' % (len(data), url))
14 start = time.time()
15 
16 gevent.joinall([
17     gevent.spawn(f, 'https://www.python.org/'),
18     gevent.spawn(f, 'https://www.yahoo.com/'),
19     gevent.spawn(f, 'https://github.com/'),
20 ])
21 
22 print(time.time()-start)

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只是简单讲主页的数据全爬了一遍没做处理。