Python wait until data is in sys.stdin

Question

my problem is the following:

My pythons script receives data via sys.stdin, but it needs to wait until new data is available on sys.stdin.

As described in th

Answer 1

I know I am bringing old stuff to life, but this seems to be one of the top hits on the topic. The solution Abalus has settled for has fixed time.sleep each cycle, regardles if the stdin is actually empty and the program should be idling or there are a lot of lines waiting to be processed. A small modification makes the program process all messages rapidly and wait only if the queue is actually empty. So only one line that arrives during the sleep period can wait, the others are processed without any lag.

This example is simply reversing the input lines, if you submit only one line it responds in a second (or whatever your sleep period is set), but can also process something like "ls -l | reverse.py" really quickly. The CPU load for such approach is minimal even on embedded systems like OpenWRT.

import sys
import time

while True:
  line=sys.stdin.readline().rstrip()
  if line:       
    sys.stdout.write(line[::-1]+'\n')
  else:
    sys.stdout.flush()
    time.sleep(1)