stdin_example.py to read from standard input

Where do I enter the code as displayed in the stdin example? Do I enter this code as a separate python file, or do I put on top of my program code, or maybe at the end of my program code? One of the code examples is:

import sys
for line in sys.stdin:
    if 'Exit' == line.rstrip():
        break
    print(f'Processing Message from sys.stdin *****{line}*****' )
print("Done")

This is one of the codes, so where do I place this code. Thank you.