Using the REPL

The REPL — Read, Evaluate, Print, Loop — is the interactive prompt you see when you start MP.EXE with no script argument.

MicroPython uc386-triage on 2026-05-01; uc386-dos with i386
Type "help()" for more information.
>>>

Anything you type at >>> is compiled and executed immediately.

Basic use

>>> 2 + 2
4
>>> name = 'World'
>>> print('hello, ' + name)
hello, World
>>> import sys
>>> sys.implementation
(name='micropython', version=(1, 26, 0), _machine='uc386-dos with i386', _mpy=4358)

Multi-line statements start a continuation prompt ... and require an empty line (or the next line at zero indentation) to finish:

>>> def double(x):
...     return x * 2
...
>>> double(21)
42

Paste mode

When you feed large blocks of code to the REPL (especially from a script file via redirection or COM1), use paste mode so MP doesn’t try to parse line-by-line:

Press Ctrl-E to enter paste mode. The prompt changes to ===.
Paste / type the full block, including blank lines.
Press Ctrl-D to finish. MP compiles the whole block at once and runs it.

>>>
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== def fib(n):
===     if n < 2: return n
===     return fib(n-1) + fib(n-2)
===
=== print([fib(i) for i in range(10)])
===
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
>>>

The bundled rigs (rigs/ssh-rig/, rigs/tls-rig/) use paste mode to feed test scripts into MP over the QEMU/DOSBox serial line.

Key bindings

The REPL emulates a small subset of GNU readline:

Ctrl-A / Ctrl-E — start / end of line
Ctrl-B / Ctrl-F — character left / right
Ctrl-D — exit REPL (on an empty line) / finish paste mode
Ctrl-C — interrupt (raises KeyboardInterrupt)
Ctrl-K — kill to end of line
Ctrl-U — kill to start of line
Backspace / Ctrl-H — delete character to the left
Up / Down — history (last entry only, no full ring buffer)

History is not persistent across REPL sessions.

Running scripts

Three ways to run a Python file:

a) Pipe into stdin

A:\> MP.EXE < HELLO.PY

The script runs to completion; MP exits when stdin closes. Output appears on the same console.

b) `import` the module

If HELLO.PY sits in the current directory, just import it:

>>> import HELLO
hello from DOS

The first import runs the module’s top-level statements. Later imports are no-ops (the module is cached in sys.modules).

c) `exec()` a file’s contents

>>> with open('HELLO.PY') as f:
...     exec(f.read())
...
hello from DOS

Useful when you want the script to run as if pasted at the REPL — its globals end up in your interactive namespace.

Stopping a runaway program

Press Ctrl-C. MP raises KeyboardInterrupt at the next bytecode instruction. If the program is in a tight C-level loop (e.g. time.sleep(60) or a blocking socket.recv), Ctrl-C may have to wait until the call returns.

If MP itself is wedged (no Ctrl-C response, no prompt), you’re looking at a real bug — file an issue at https://github.com/avwohl/freedos_micro_python/issues with whatever output you have.

Exiting

>>> import sys
>>> sys.exit()

Or press Ctrl-D at an empty prompt. MP returns to DOS with the exit code you passed (default 0).

>>> sys.exit(2)

returns exit code 2 to the parent (DOS BATCH IF ERRORLEVEL 2).

When something goes wrong

An unhandled exception prints the traceback and drops you back at >>>.
A syntax error prints the line + caret position.
sys.tracebacklimit = N caps traceback depth (handy on a small screen).

>>> def f(): g()
>>> def g(): raise ValueError('boom')
>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in f
  File "<stdin>", line 1, in g
ValueError: boom
>>>