so I want to put Python in a pipe where it reads from std in , does something, writes to std out:
$ cat test.py
#!/usr/bin/env python3
import sys
# https://stackoverflow.com/questions/1450393/how-do-i-read-from-stdin
for n,line in enumerate(sys.stdin):
a=line.split()
if n%5==0:
sys.stdout.write(line)
