Question

我正在尝试从子进程的输出中捕获一个字符串，当子进程请求用户输入时，在字符串中包含用户输入，但我无法使stdout工作。

我使用while循环从stdout获取字符串输出，但我不知道如何在读取字符串后终止它。

我尝试使用subprocess.check_output，但后来我看不到用户输入的提示。

import subprocess
import sys
child = subprocess.Popen(["java","findTheAverage"], stdout = subprocess.PIPE, stdin = subprocess.PIPE )
string = u""

while True:
    line = str(child.stdout.read(1))
    if line != '':
        string += line[2]
        print(string)
    else:
        break

print(string)
for line in sys.stdin:
    print(line)
    child.stdin.write(bytes(line, 'utf-8'))

编辑：

借助Alfe发布的帮助和代码，我现在有一个从子进程程序输出创建的字符串，以及用户输入到该程序，但它混乱不堪。

字符串似乎首先得到输出的第一个字母，然后是用户输入，然后是输出的其余部分。

字符串混乱的例子：

U2
3ser! please enter a double:U
4ser! please enter another double: U
5ser! please enter one final double: Your numbers were:
a = 2.0
b = 3.0
c = 4.0
average = 3.0

意思是：

User! please enter a double:2
User! please enter another double: 3
User! please enter one final double: 4
Your numbers were:
a = 2.0
b = 3.0
c = 4.0
average = 3.0

使用代码：

import subprocess
import sys
import signal
import select


def signal_handler(signum, frame):
    raise Exception("Timed out!")


child = subprocess.Popen(["java","findTheAverage"], universal_newlines = True, stdout = subprocess.PIPE, stdin = subprocess.PIPE )
string = u""
stringbuf = ""

while True:
  print(child.poll())
  if child.poll() != None and not stringbuf:
    break
  signal.signal(signal.SIGALRM, signal_handler)
  signal.alarm(1)
  try:
    r, w, e = select.select([ child.stdout, sys.stdin ], [], [])
    if child.stdout in r:
        stringbuf = child.stdout.read(1)
        string += stringbuf
        print(stringbuf)
  except:
    print(string)
    print(stringbuf)
  if sys.stdin in r:
    typed = sys.stdin.read(1)
    child.stdin.write(typed)
    string += typed

最终编辑：

好吧，我玩了它并使用了这段代码：

import subprocess
import sys
import select
import fcntl
import os

# the string that we will return filled with tasty program output and user input #
string = ""

# the subprocess running the program #
child = subprocess.Popen(["java","findTheAverage"],bufsize = 0, universal_newlines = True, stdout = subprocess.PIPE, stdin = subprocess.PIPE )

# stuff to stop IO blocks in child.stdout and sys.stdin ## (I stole if from  http://stackoverflow.com/a/8980466/2674170)
fcntl.fcntl(child.stdout.fileno(), fcntl.F_SETFL, os.O_NONBLOCK)
fcntl.fcntl(sys.stdin.fileno(), fcntl.F_SETFL, os.O_NONBLOCK)

# this here in the unlikely event that the program has #
# finished by the time the main loop is first running  #
# because if that happened the loop would end without  #
# having added the programs output to the string!      #
progout = ""
typedbuf = "#"

### here we have the main loop, this friendly fellah is 
### going to read from the program and user, and tell
### each other what needs to be known
while True:

## stop when the program finishes and there is no more output
  if child.poll() != None and not progout:
    break

# read from 
  typed = ""

  while typedbuf:
    try:
      typedbuf = sys.stdin.read(1)
    except:
      break
    typed += typedbuf
    stringbuf  = "#"
  string += typed
  child.stdin.write(typed)

  progout = ""
  progoutbuf = "#"
  while progoutbuf:
    try:
      progoutbuf = child.stdout.read(1)
    except:
      typedbuf = "#"
      break 
    progout += progoutbuf
  if progout:
    print(progout)
  string += progout

# the final output string #
print( string)

Answer 1

您需要select同时从多个源读取（在您的情况下是stdin和子进程的输出）。

import select

string = ''
while True:
  r, w, e = select.select([ child.stdout, sys.stdin ], [], [])
  if child.stdout in r:
    string += child.stdout.read()
  if sys.stdin in r:
    typed = sys.stdin.read()
    child.stdin.write(typed)
    string += typed

您仍然需要找到适当的破坏条件才能离开该循环。但你可能已经明白了这个想法。

我想在这一点上发出警告：写入管道的进程通常会缓冲到最新的可能时刻;您可能没想到这一点，因为当从命令行（在终端中）测试相同的程序时，通常只有行被缓冲。这是出于性能考虑。写入终端时，用户通常希望尽快看到输出。在写入管道时，通常情况下，阅读过程很乐意给予更大的块，以便在它们到达之前睡得更久。

使用程序所需的用户输入从程序中获取输出

1 个答案: