Python 2 vs Python 3:

The key differences between Python 2.7.x and Python 3.x with examples
by sebastian raschka

Python 2 vs Python 3: Key Differences

Important differences between Python 2.x and Python 3.x with examples - GeeksforGeeks

Python 2.7 Countdown clock

What’s New In Python 3.0 — Python 3.8.0 documentation