Sampling program to read write every X lines to stderr, otherwise, just read from stdin and write to stdout (useful for monitoring stream progress)

sample_tree.py

#!/usr/bin/env python

import sys
import datetime

rate = 100000

if len(sys.argv) > 1:
    rate = int(sys.argv[1])

i = 0
for line in sys.stdin:
    i += 1
    if i > rate:
        sys.stderr.write('\n%s\n' % datetime.datetime.now())
        sys.stderr.write(line)
        i = 0
    sys.stdout.write(line)