How to pipe input to python line by line from linux program?

What you want is popen, which makes it possible to directly read the output of a command like you would read a file:

import os
with os.popen('ps -ef') as pse:
    for line in pse:
        print line
        # presumably parse line now

Note that, if you want more complex parsing, you'll have to dig into the documentation of subprocess.Popen.

Instead of using command line arguments I suggest reading from standard input (stdin). Python has a simple idiom for iterating over lines at stdin:

import sys

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

My usage example (with above's code saved to iterate-stdin.py):

$ echo -e "first line\nsecond line" | python iterate-stdin.py 
first line
second line

With your example:

$ echo "days go by and still" | python iterate-stdin.py
days go by and still