Popen.stdout.readline（）在Python 3.2中工作，但在Python 3.6中返回空字符串

Question

I am using Popen to start a telnet process over ssh, send commands through the telnet and check the process for output to monitor the state of the telnet. The weird thing I encountered is that the code works fine with Python 3.2.3 but when I run it in Python 3.6.5 with no code changes, it fails to get the output.

I have tried

• flushing the stdout

• waiting up to 10s after stdout.write

• checked stderr

def nonblockingread(sout):
   fd = output.fileno()
   fl = fcntl.fcntl(fd, fcntl.F_GETFL)
   try:
       return sout.read()
   except:
       return ""

process = Popen(shlex.split("ssh anon@server \"telnet 0 2323\""), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
print(nonblockingread(process.stdout)) # works for both versions
process.stdin.write(b"start service 4\n")
print(nonblockingread(process.stdout)) # works in 3.2 but not 3.6 (prints empty line)
print(process.stdout.readline()) # also prints empty line in 3.6

Answer 1

默认情况下，在3.2.4和3.3.1中打开了缓冲，在Python 3中无意中关闭了。您需要将write flush到process.stdin ，以便另一方看到任何内容。