This is the documentation for the latest development branch of MicroPython and may refer to features that are not available in released versions.

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Quick reference for the UNIX and Windows ports

Command line options


micropython [ -h ] [ -i ] [ -O<level> ] [ -v ] [ -X <option> ] [ -c <command> | -m <module> | <script> ] [ <args> ]

Invocation options:

-c <command>

Runs the code in <command>. The code can be one or more Python statements.

-m <module>

Runs the module <module>. The module must be in sys.path.


Runs the file <script>. The script must be a valid MicroPython source code file.

If none of the 3 options above are given, then MicroPython is run in an interactive REPL mode.


Any additional arguments after the module or script will be passed to sys.argv (not supported with the -c option).

General options:


Prints a help message containing the command line usage and exits.


Enables inspection. When this flag is set, MicroPython will enter the interactive REPL mode after the command, module or script has finished. This can be useful for debugging the state after an unhandled exception. Also see the MICROPYINSPECT environment variable.

-O | -O<level> | -OO...

Sets the optimization level. The O can be followed by a number or can be repeated multiple times to indicate the level. E.g. -O3 is the same as -OOO.


Increases the verbosity level. This option can be given multiple times. This option only has an effect if MICROPY_DEBUG_PRINTERS was enabled when MicroPython itself was compiled.

-X <option>

Specifies additional implementation-specific options. Possible options are:

  • -X compile-only compiles the command, module or script but does not run it.

  • -X emit={bytecode,native,viper} sets the default code emitter. Native emitters may not be available depending on the settings when MicroPython itself was compiled.

  • -X heapsize=<n>[w][K|M] sets the heap size for the garbage collector. The suffix w means words instead of bytes. K means x1024 and M means x1024x1024.

  • -X realtime sets thread priority to realtime. This can be used to improve timer precision. Only available on macOS.

Environment variables


Overrides the default search path for MicroPython libraries. MICROPYPATH should be set to a colon (semicolon for Windows port) separated list of directories. If MICROPYPATH is not defined, the search path will be ~/.micropython/lib:/usr/lib/micropython (~/.micropython/lib for Windows port) or the value of the MICROPY_PY_SYS_PATH_DEFAULT option if it was set when MicroPython itself was compiled.


Enables inspection. If MICROPYINSPECT is set to a non-empty string, it has the same effect as setting the -i command line option.