A REPL (say it, “REP-UL”) is an interactive way to talk to your computer in Python. To make this work, the computer does four things:
Read the user input (your Python commands).
Evaluate your code (to work out what you mean).
Print any results (so you can see the computer’s response).
Loop back to step 1 (to continue the conversation).
Mu is a simple code editor that works with the Adafruit CircuitPython boards.
for the installation, please refer the Adafruit tutorial from https://learn.adafruit.com/welcome-to-circuitpython/installing-mu-editor