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应用将其转发到scala解释器。执行命令后，应用程序将显示操作结果。

这个想法是用来Popen创建一个管道，通过该管道我可以发送命令并读取结果。这个想法很简单，但是没有用。我不明白的是，为什么在sys.stdin打开管道后它们不再起作用。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

您需要从scala启动时开始读取所有行，然后以新行输入命令，并在获得以下两行输出之后：

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

为了使它能够通过使用不带缓冲区的bash运行，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，则可能应该使用：

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

从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 >>>

有关外壳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