How do I write a unix filter in python?

Question

I want to write a program that reads stdin (unbuffered) and writes stdout (unbuffered) doing some trivial char-by-char transformation. For the sake of the example let\'s say

Answer 1

Use the -u switch for the python interpreter to make all reads and writes unbuffered. Similar to setting $| = true; in Perl. Then proceed as you would, reading a line modifying it and then printing it. sys.stdout.flush() not required.

#!/path/to/python -u

import sys

for line in sys.stdin:
    process_line(line)