這次看了一些關(guān)于協(xié)程(coroutine)的資料，這是python特有的，我會(huì)在這篇文字里面慢慢總結(jié)整理下來，估計(jì)會(huì)寫個(gè)1周多。

coroutine和generator的關(guān)系

generator用到了yield語法，而coroutine也是用到了yield語法，什么區(qū)別呢？大致是這樣的：

1. generator是為iteration產(chǎn)生數(shù)據(jù)
2. coroutine是消費(fèi)數(shù)據(jù)
3. coroutine也可以產(chǎn)生值，但目的不是為了迭代
4. 不要把2個(gè)概念混在一起，寫出讓大家摸不著頭腦的代碼

下面的代碼是generator，用來倒數(shù)迭代用

# countdown.py
#
# A simple generator function

def countdown(n):
    print "Counting down from", n
    while n > 0:
        yield n
        n -= 1
    print "Done counting down"

# Example use
if __name__ == '__main__':
    for i in countdown(5):
        print i

輸出是

Counting down from 5
5
4
3
2
1
Done counting down

下面代碼是coroutine，用來消費(fèi)字符串，過濾出有用的行

# grep.py
#
# A very simple coroutine

def grep(pattern):
    print "Looking for %s" % pattern
    while True:
        line = (yield)
        if pattern in line:
            print line,

# Example use
if __name__ == '__main__':
    g = grep("python")
    # g.send(None)
    g.next()
    g.send("Yeah, but no, but yeah, but no")
    g.send("A series of tubes")
    g.send("python generators rock!")
    g.close()

輸出是

Looking for python
python generators rock!

千萬不要寫下面的代碼，又想消費(fèi)，又想迭代，結(jié)果不知所云：

# bogus.py
#
# Bogus example of a generator that produces and receives values


def countdown(n):
    print "Counting down from", n
    while n >= 0:
        newvalue = (yield n)
        # If a new value got sent in, reset n with it
        if newvalue is not None:
            n = newvalue
        else:
            n -= 1

# The holy grail countdown
c = countdown(5)
for x in c:
    print x
    if x == 5:
        c.send(3)

輸出是：

Counting down from 5
5
2
1
0