tags | read lines from stdin

$ cat count_lines.py
import sys
data = sys.stdin.readlines()
print("Counted", len(data), "lines.")

$ cat count_lines.py | python count_lines.py
Counted 3 lines.

Ref:-

• https://stackoverflow.com/a/1450396
• Used this technique to answer https://unix.stackexchange.com/questions/743855/convert-only-all-uppercase-lines-to-lower-case