Tee does not show output or write to file

Question

I wrote a python script to monitor the statuses of some network resources, an infinite pinger if you will. It pings the same 3 nodes forever until it receives a keyboard interrupt. I tried using tee to redirect the output of the program to a file, but it does not work:

λ sudo ./pingster.py  15:43:33        node1 SUCESS | node2 SUCESS | node3 SUCESS 15:43:35        node1 SUCESS | node2 SUCESS | node3 SUCESS 15:43:36        node1 SUCESS | node2 SUCESS | node3 SUCESS 15:43:37        node1 SUCESS | node2 SUCESS | node3 SUCESS 15:43:38        node1 SUCESS | node2 SUCESS | node3 SUCESS ^CTraceback (most recent call last):   File "./pingster.py", line 42, in <module>     main()   File "./pingster.py", line 39, in main     sleep(1) KeyboardInterrupt  λ sudo ./pingster.py | tee ping.log # wait a few seconds ^CTraceback (most recent call last):   File "./pingster.py", line 42, in <module>     main()   File "./pingster.py", line 39, in main     sleep(1) KeyboardInterrupt  λ file ping.log ping.log: empty  

I am using colorama for my output, I thought that perhaps could be causing the issue, but I tried printing something before I even imported colorama, and the file is still empty. What am I doing wrong here?

Edit: Here is the python file I'm using

#!/home/nate/py-env/ping/bin/python  from __future__ import print_function from datetime import datetime from collections import OrderedDict from time import sleep  import ping import colorama   def main():     d = {         'node1': '10.0.0.51',         'node2': '10.0.0.50',         'node3': '10.0.0.52',     }     addresses = OrderedDict(sorted(d.items(), key=lambda t: t[0]))      colorama.init()     while True:         status = []         time = datetime.now().time().strftime('%H:%M:%S')         print(time, end='\t')         for location, ip_address in addresses.items():             loss, max_time, avg_time = ping.quiet_ping(ip_address, timeout=0.5)             if loss < 50:                 status.append('{0} SUCESS'.format(location))             else:                 status.append(                     '{}{} FAIL{}'.format(                         colorama.Fore.RED,                         location,                         colorama.Fore.RESET,                     )                 )         print(' | '.join(status))         sleep(1)  if __name__ == '__main__':     main() 

Answer 1

Here's a simpler way of reproducing your issue:

$ cat foo.py from time import sleep while True:    sleep(2)   print "hello"  $ python foo.py hello hello     (...)  $ python foo.py | tee log (no output) 

This happens because python buffers stdout when it's not a terminal. The easiest way to unbuffer it is to use python -u:

$ python -u foo.py | tee log hello hello (...) 

You can also set the shebang to #!/usr/bin/python -u (this does not work with env).