pick.py

import sys

if len(sys.argv) < 2:
  print("""Usage:
  pick.py data.txt [lines_to_skip = 0] [first_line = 0]""")
  sys.exit(0)

file = sys.argv[1]
skip = int(sys.argv[2]) + 1 if len(sys.argv) > 2 else 1
start = int(sys.argv[3]) if len(sys.argv) > 3 else 0

with open(file, "r") as f:
  lines = f.read().strip().split("\n")
  for i in range(skip):
    for line in lines[start::skip]:
      print(line.strip())
    start = start + 1