python stdout flush and tee
Question: The following code ends with broken pipe when piped into tee, but behave
correctly when not piped :

    
    
    #!/usr/bin/python
    import sys
    def testfun():
        while 1:
            try :
                s = sys.stdin.readline()
            except(KeyboardInterrupt) :
                print('Ctrl-C pressed')
                sys.stdout.flush()
                return
            print s
    
    if __name__ == "__main__":
        testfun()
        sys.exit()
    

Expected output :

    
    
    ./bug.py 
    Ctrl-C pressed
    

What is observed when piped into tee is either a broken pipe or no output at
all, ie nothing on tee stdout, and nothing in bug.log :

    
    
    ./bug.py | tee bug.log
    Traceback (most recent call last):
      File "./bug.py", line 14, in <module>
        sys.stdout.flush()
    IOError: [Errno 32] Broken pipe
    

What can be the reason for this ?


Answer: Nope, hitting Ctrl-C does NOT terminate both processes. It terminates the tee
process only, the end of the tee process close the pipe between your script
and tee, and hence your script dies with the broken pipe message.

To fix that, tee has an option to pass the Ctrl-C to its previous process in
the pipe: -i

try: man tee

    
    
    ./bug.py
    ^CCtrl-C pressed
    ./bug.py | tee log
    ^CTraceback (most recent call last):
      File "./bug.py", line 14, in <module>
        testfun()
      File "./bug.py", line 9, in testfun
        sys.stdout.flush()
    IOError: [Errno 32] Broken pipe
    
    ./bug.py | tee -i log
    ^CCtrl-C pressed
    

