unbuffered stdout in python (as in python -u) from within the program

Question

Is there any way to get the effect of running python -u from within my code? Failing that, can my program check if it is running in -u mode and exit with an error message if not? This is on linux (ubuntu 8.10 server)

Answer 1

Assuming you're on Windows:

msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)

Answer 2

I think this question has already been answered on SO:

import sys
sys.stdout.flush()

(Although you probably want to do this without constantly flushing sys.stdout?)

Answer 3

You might use the fact that stderr is never buffered and try to redirect stdout to stderr:

    import sys
    #buffered output is here
    doStuff()

    oldStdout = sys.stdout
    sys.stdout = sys.stderr
    #unbuffered output from here on

    doMoreStuff()
    sys.stdout = oldStdout

    #the output is buffered again
    doEvenMoreStuff()

Answer 4

The best I could come up with:

>>> import os
>>> import sys
>>> unbuffered = os.fdopen(sys.stdout.fileno(), 'w', 0)
>>> unbuffered.write('test')
test>>> 
>>> sys.stdout = unbuffered
>>> print 'test'
test

Tested on GNU/Linux. It seems it should work on Windows too. If I knew how to reopen sys.stdout, it would be much easier:

sys.stdout = open('???', 'w', 0)

References:
http://docs.python.org/library/stdtypes.html#file-objects
http://docs.python.org/library/functions.html#open
http://docs.python.org/library/os.html#file-object-creation

[Edit]

Note that it would be probably better to close sys.stdout before overwriting it.

Answer 5

You could always pass the -u parameter in the shebang line:

#!/usr/bin/python -u