===== read from stdin =====
tags | read lines from stdin

==== approach 1 ====
using fileinput
<code>
$ cat count_lines.py
import fileinput

with fileinput.input() as f:
    count = 0
    for line in f:
      count += 1

print('counted ', count, ' lines.')
</code>

<code>
$ python ./count_lines.py < ./count_lines.py
counted  8  lines.
</code>

<code>
$ wc -l ./count_lines.py
8 ./count_lines.py
</code>

==== approach 2 ====
using sys.stdin
<code>
$ cat count_lines.py
import sys
data = sys.stdin.readlines()
print("Counted", len(data), "lines.")
</code>

<code>
$ cat count_lines.py | python count_lines.py
Counted 3 lines.
</code>

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