Streaming pipes in Python

I'm trying to convert the output of vmstat into a CSV file using Python, so I use something like this to convert to CSV and add the date and time as coloumns:

vmstat 5 | python myscript.py >> vmstat.log

The problem I'm having is it blocks while trying to iterate sys.stdin. It seems like the input buffer doesn't get flushed. I don't want to endlessly loop around and burn processor time as I'm trying to measure this. H开发者_JAVA技巧ere's a simple demonstration which blocks on line 3:

import sys

for line in sys.stdin:
    sys.stdout.write(line)
    sys.stdout.flush()

Is there an easy way to access the stream immediately like grep does, without pausing while the input buffer fills up?

VMstat 5,does not close the stdout, so the python buffer is still waiting for more data.

Use this instead:

for line in iter(sys.stdin.readline, ""):
    print line