check if input is available on stdin with timeout

Question

I have a python script that publishes messages that are read from stdin onto a message queue in the network. However, if there wasn't any message on the pipe for a specified amount of time I have to send a heartbeat.

So I have to distinguish between 3 cases:

There is input on the pipe that can be processed
There was no input for some specified amount of time
The piping process has been closed and we can gracefully terminate.

Currently, my code looks as follow:

import sys
for i, line in enumerate(sys.stdin):
    connection.publish(line)
connection.close()

However I need to interrupt the for look if there was any timeout. I.e. sys.stdin has not delivered any data for some time.

score 5 · Accepted Answer · edited Feb 07 '22 at 16:35

5

This is what I finally came up with

import sys
import select


while True:
    try:
        if select.select([sys.stdin,],[],[],2.0)[0]:
            line = sys.stdin.next()
            print "Got:", line
        else:
            print "No data for 2 secs"

    except StopIteration:
        print 'EOF!'
        break

edited Feb 07 '22 at 16:35

Neuron

5,141
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answered Jan 07 '17 at 12:44

worenga

5,776
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50

If you're using Python 3, use sys.stdin.readline(). – srdecny Sep 16 '21 at 09:30
Also, with python3, stdin.readline() returns '\n' on an empty line, but '' on EOF, so use that to check for EOF instead of a StopIteration exception. – petiepooo Jul 19 '22 at 15:31
Does this actually check whether a new *line* is available or just any content? – MisterMiyagi Oct 07 '22 at 11:08

ChrisB · Answer 2 · 2023-03-15T14:41:11.227

If anybody is looking for a portable solution, this is what I came up with after lots of trial and error. It requires the pywin32 pypi package to work on windows

import os, sys

if sys.platform == "win32":
    import win32api, win32event, win32file, pywintypes
else:
    import select

def stdin_has_content(timeout: float) -> bool:
    assert timeout >= 0
    if sys.platform == "win32":
        try:
            # without this flush, WaitForSingleObject might return early
            win32file.FlushFileBuffers(win32api.STD_INPUT_HANDLE)
        except pywintypes.error:         
            pass # this happens if stdin is already closed, but that's ok
        return win32event.WaitForSingleObject(
            win32api.STD_INPUT_HANDLE, int(timeout * 1000)
        ) == win32event.WAIT_OBJECT_0       
    else:
        rlist, _, _ = select.select([sys.stdin], [], [], timeout)
        return bool(rlist)

check if input is available on stdin with timeout

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