flush library function on
sys.stdout which is the STDOUT:
From python doc:
Flush the write buffers of the stream if applicable.
This does nothing for read-only and non-blocking streams.
If you can't change the code while you can change the
python interpreter options used, you can give it
Force stdin, stdout and stderr to be totally unbuffered. On
systems where it matters, also put stdin, stdout and stderr
in binary mode. Note that there is internal buffering in
xreadlines(), readlines() and file-object iterators ("for
line in sys.stdin") which is not influenced by this option.
To work around this, you will want to use
"sys.stdin.readline()" inside a "while 1:" loop.
If you can't change the interpreter options either, there is another way too by setting the environment variable
If this is set to a non-empty string it is equivalent to
specifying the -u option.
Reference: python2.7 manual