First Steps

There are three ways to run MicroPython, and they are the same three as CPython: type at it interactively, hand it a file, or pass it a one-liner. On a microcontroller the interactive way is the famous one — you connect to the chip and type Python at it live — but it works identically here, so learn it here.

The REPL

Start micropython with no arguments in a terminal and you get the REPL (read–eval– print loop), captured from the lab:

MicroPython v1.29.0 on 2026-10-21; linux [GCC 13.3.0] version
Type "help()" for more information.
>>> 2 + 3
5
>>> name = "fern"
>>> print(name.upper(), len(name))
FERN 4
>>> import sys
>>> sys.implementation.name
'micropython'

Three things to notice. The banner names the build, as in chapter 1. The prompt is >>>, inherited from CPython. And a bare expression — 2 + 3, sys.implementation.name — prints its value. That echo belongs to the REPL only: in a script file, an expression on its own line computes quietly and prints nothing, in both Pythons. Half of all beginner confusion ("it worked when I typed it, not in my file") is exactly this difference.

(The lab captured this through a pseudo-terminal, because the REPL only appears when MicroPython is talking to a terminal; piping lines into it runs them as a script instead. On your own machine just open a terminal and type micropython.)

A script file

examples/first_steps.py — a station name, five readings, four summary lines:

$ micropython fixtures/first_steps.py
Station: greenhouse
Readings: 5
Warmest: 24.5
Coolest: 18.5
Average: 21.3

$ python3 fixtures/first_steps.py
Station: greenhouse
Readings: 5
Warmest: 24.5
Coolest: 18.5
Average: 21.3

Same file, same output, no changes. Most of this guide is about the cases where that stops being true — but it is worth starting from the fact that ordinary Python is ordinary Python.

One-liners

micropython -c "..." runs a snippet directly, which is how the lab takes most of its measurements (-c is CPython's flag too):

$ micropython -c "import sys; print(sys.platform)"
linux

Check: micropython alone should drop you at a >>> prompt; typing 1 + 1 should answer 2; Ctrl-D (or Ctrl-C then Ctrl-D on some systems) leaves. If instead the program ends immediately with no prompt, you are not in a terminal — something piped it.