What is the small but useful code that you ever written?

Question

we face many problems in our programming career but sometimes a simple small script can save us from that problem. Share The Useful code with world.

bellow is mine,
(a password generation script)

https://code.sololearn.com/cG1WPZv2E2Od/?ref=app

Answer 1

Here is a complete calculator.

https://code.sololearn.com/ck9rtCKNCAdK/?ref=app

Answer 2

I don't have it on here, but one of my first useful Python scripts was a program I wrote to sort over 5,000 Rom files down to the 1200ish I actually needed. It was 12 lines of code and worked amazingly. Sometimes small and simple is perfect