与popen python一起使用时,输入命令似乎不起作用

Question

我正在编写一个执行scala命令的小型python应用程序.用户可以通过STDIN插入命令,然后python应用程序将它们转发给scala解释器.执行命令后,应用程序将显示操作结果.

我的想法是用来Popen创建一个管道,我可以通过它发送命令和读取结果.这个想法很简单,但它不起作用.我不明白的是,为什么sys.stdin管道打开后它不再起作用了.这使得无法在python中读取命令.

这是我正在使用的代码:

import sys
from subprocess import Popen, PIPE

with Popen(["scala"], stdout=PIPE, stdin=PIPE, bufsize=0, universal_newlines=True) as scala:
    while True:
        print("Enter scala command >>> ", end="")
        sys.stdout.flush()
        command = input()
        scala.stdin.write(command)
        scala.stdin.flush()
        print(scala.stdout.readline())

Answer 1

您需要读取 scala 启动时的所有行，然后换行输入命令并获取以下两行输出：

from subprocess import Popen, PIPE

with Popen(["scala"], stdout=PIPE, stdin=PIPE, bufsize=0, universal_newlines=True) as scala:
    for line in scala.stdout:
        print(line)
        if not line.strip():
            break
    while True:
        command = input("Enter scala command >>> \n")
        scala.stdin.write(command+"\n")
        scala.stdin.flush()
        for line in scala.stdout:
            if not line.strip():
                break
            print(line)

运行示例：

Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_60).

Type in expressions to have them evaluated.

Type :help for more information.



Enter scala command >>> 3+4
scala> 3+4

res0: Int = 7

Enter scala command >>> 4 * 4
scala> 4 * 4

res1: Int = 16

Enter scala command >>> 16 / 4
scala> 16 / 4

res2: Int = 4

要让它在 bash 中工作，使用unbuffer运行它似乎可以解决输出问题：

from subprocess import Popen, PIPE

with Popen(["unbuffer", "-p","scala"], stdout=PIPE, stdin=PIPE, bufsize=0, universal_newlines=True) as scala:
    for line in scala.stdout:
        print(line)
        if not line.strip():
            break
    while True:
        command = input("Enter scala command >>> ")
        scala.stdin.write(command+"\n")
        scala.stdout.flush()
        for line in scala.stdout:
            if not line.strip():
                break
            print(line)

如果您使用的是 Mac Os x，您可能应该使用：

with Popen(["script", "-q", "/dev/null", "scala"], stdout=PIPE, stdin=PIPE, bufsize=0, universal_newlines=True) as scala:

来自bash：

        print(line)
## -- End pasted text --
Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_60).

Type in expressions to have them evaluated.

Type :help for more information.



Enter scala command >>> 4 + 2
scala> 4 + 2

res0: Int = 6

Enter scala command >>> 4 * 12
scala> 4 * 12

res1: Int = 48

Enter scala command >>> 100 // 25
scala> 100 // 25

res2: Int = 100

Enter scala command >>> 

有关 shell 缓冲区问题的更多信息：

• http://www.pixelbeat.org/programming/stdio_buffering/
• https://unix.stackexchange.com/questions/25372/turn-off-buffering-in-pipe