python标准库介绍——36 popen2 模块详解

==popen2 模块==
 
``popen2`` 模块允许你执行外部命令, 并通过流来分别访问它的 ``stdin`` 和 ``stdout`` ( 可能还有 ``stderr`` ). 
 
在 python 1.5.2 以及之前版本, 该模块只存在于 Unix 平台上. 2.0 后, Windows 下也实现了该函数.
[Example 3-9 #eg-3-9] 展示了如何使用该模块来给字符串排序. 
 
====Example 3-9. 使用 popen2 模块对字符串排序Module to Sort Strings====[eg-3-9]
 
```
File: popen2-example-1.py
 
import popen2, string
 
fin, fout = popen2.popen2("sort")
 
fout.write("foo\n")
fout.write("bar\n")
fout.close()
 
print fin.readline(),
print fin.readline(),
fin.close()
 
*B*bar
foo*b*
```
 
[Example 3-10 #eg-3-10] 展示了如何使用该模块控制应用程序 .
 
====Example 3-10. 使用 popen2 模块控制 gnuchess====[eg-3-10]
 
```
File: popen2-example-2.py
 
import popen2
import string
 
class Chess:
    "Interface class for chesstool-compatible programs"
 
    def _ _init_ _(self, engine = "gnuchessc"):
        self.fin, self.fout = popen2.popen2(engine)
        s = self.fin.readline()
        if s != "Chess\n":
            raise IOError, "incompatible chess program"
 
    def move(self, move):
        self.fout.write(move + "\n")
        self.fout.flush()
        my = self.fin.readline()
        if my == "Illegal move":
            raise ValueError, "illegal move"
        his = self.fin.readline()
        return string.split(his)[2]
 
    def quit(self):
        self.fout.write("quit\n")
        self.fout.flush()
 
#
# play a few moves
 
g = Chess()
 
print g.move("a2a4")
print g.move("b2b3")
 
g.quit()
 
*B*b8c6
e7e5*b*
```