Lê o stdin e para cada linha imprime a diferença de tempo.

deltat.py

from __future__ import print_function

import sys
import time


def main():
    t0 = time.time()

    while 1:
        try:
            line = sys.stdin.readline()
            now = time.time()
            d, t0 = now - t0, now

            print(line, end='')
            print('+%ss' % (d), file=sys.stderr)

        except KeyboardInterrupt:
            break

if __name__ == '__main__':
    main()