.. glossary::
baremetal
A system without a (full-fledged) operating system, for example an
:term:`MCU`-based system. When running on a baremetal system,
MicroPython effectively functions like a small operating system,
running user programs and providing a command interpreter
(:term:`REPL`).
buffer protocol
Any Python object that can be automatically converted into bytes, such
as ``bytes``, ``bytearray``, ``memoryview`` and ``str`` objects, which
all implement the "buffer protocol".
board
Typically this refers to a printed circuit board (PCB) containing a
:term:`microcontroller <MCU>` and supporting components.
MicroPython firmware is typically provided per-board, as the firmware
contains both MCU-specific functionality but also board-level
functionality such as drivers or pin names.
bytecode
A compact representation of a Python program that generated by
compiling the Python source code. This is what the VM actually
executes. Bytecode is typically generated automatically at runtime and
is invisible to the user. Note that while :term:`CPython` and
MicroPython both use bytecode, the format is different. You can also
pre-compile source code offline using the :term:`cross-compiler`.
callee-owned tuple
This is a MicroPython-specific construct where, for efficiency
reasons, some built-in functions or methods may reuse the same
underlying tuple object to return data. This avoids having to allocate
a new tuple for every call, and reduces heap fragmentation. Programs
should not hold references to callee-owned tuples and instead only
extract data from them (or make a copy).
CircuitPython
A variant of MicroPython developed by `Adafruit Industries
<https://circuitpython.org>`_.
CPython
CPython is the reference implementation of the Python programming
language, and the most well-known one. It is, however, one of many
implementations (including Jython, IronPython, PyPy, and MicroPython).
While MicroPython's implementation differs substantially from CPython,
it aims to maintain as much compatibility as possible.
cross-compiler
Also known as ``mpy-cross``. This tool runs on your PC and converts a
:term:`.py file` containing MicroPython code into a :term:`.mpy file`
containing MicroPython :term:`bytecode`. This means it loads faster (the board
doesn't have to compile the code), and uses less space on flash (the
bytecode is more space efficient).
driver
A MicroPython library that implements support for a particular
component, such as a sensor or display.
FFI
Acronym for Foreign Function Interface. A mechanism used by the
:term:`MicroPython Unix port` to access operating system functionality.
This is not available on :term:`baremetal` ports.
filesystem
Most MicroPython ports and boards provide a filesystem stored in flash
that is available to user code via the standard Python file APIs such
as ``open()``. Some boards also make this internal filesystem
accessible to the host via USB mass-storage.
frozen module
A Python module that has been cross compiled and bundled into the
firmware image. This reduces RAM requirements as the code is executed
directly from flash.
Garbage Collector
A background process that runs in Python (and MicroPython) to reclaim
unused memory in the :term:`heap`.
GPIO
General-purpose input/output. The simplest means to control electrical
signals (commonly referred to as "pins") on a microcontroller. GPIO
typically allows pins to be either input or output, and to set or get
their digital value (logical "0" or "1"). MicroPython abstracts GPIO
access using the :class:`machine.Pin` and :class:`machine.Signal`
classes.
GPIO port
A group of :term:`GPIO` pins, usually based on hardware properties of
these pins (e.g. controllable by the same register).
heap
A region of RAM where MicroPython stores dynamic data. It is managed
automatically by the :term:`Garbage Collector`. Different MCUs and
boards have vastly different amounts of RAM available for the heap, so
this will affect how complex your program can be.
interned string
An optimisation used by MicroPython to improve the efficiency of
working with strings. An interned string is referenced by its (unique)
identity rather than its address and can therefore be quickly compared
just by its identifier. It also means that identical strings can be
de-duplicated in memory. String interning is almost always invisible to
the user.
MCU
Microcontroller. Microcontrollers usually have much less resources
than a desktop, laptop, or phone, but are smaller, cheaper and
require much less power. MicroPython is designed to be small and
optimized enough to run on an average modern microcontroller.
micropython-lib
MicroPython is (usually) distributed as a single executable/binary
file with just few builtin modules. There is no extensive standard
library comparable with :term:`CPython`'s. Instead, there is a related,
but separate project `micropython-lib
<https://github.com/micropython/micropython-lib>`_ which provides
implementations for many modules from CPython's standard library.
Some of the modules are implemented in pure Python, and are able to
be used on all ports. However, the majority of these modules use
:term:`FFI` to access operating system functionality, and as such can
only be used on the :term:`MicroPython Unix port` (with limited support
for Windows).
Unlike the :term:`CPython` stdlib, micropython-lib modules are
intended to be installed individually - either using manual copying or
using :term:`mip`.
MicroPython port
MicroPython supports different :term:`boards <board>`, RTOSes, and
OSes, and can be relatively easily adapted to new systems. MicroPython
with support for a particular system is called a "port" to that
system. Different ports may have widely different functionality. This
documentation is intended to be a reference of the generic APIs
available across different ports ("MicroPython core"). Note that some
ports may still omit some APIs described here (e.g. due to resource
constraints). Any such differences, and port-specific extensions
beyond the MicroPython core functionality, would be described in the
separate port-specific documentation.
MicroPython Unix port
The unix port is one of the major :term:`MicroPython ports
<MicroPython port>`. It is intended to run on POSIX-compatible
operating systems, like Linux, MacOS, FreeBSD, Solaris, etc. It also
serves as the basis of Windows port. The Unix port is very useful for
quick development and testing of the MicroPython language and
machine-independent features. It can also function in a similar way to
:term:`CPython`'s ``python`` executable.
mip
A package installer for MicroPython (mip - "mip installs packages"). It
installs MicroPython packages either from :term:`micropython-lib`,
GitHub, or arbitrary URLs. mip can be used on-device on
network-capable boards, and internally by tools such
as :term:`mpremote`.
mpremote
A tool for interacting with a MicroPython device.
.mpy file
The output of the :term:`cross-compiler`. A compiled form of a
:term:`.py file` that contains MicroPython :term:`bytecode` instead of
Python source code.
native
Usually refers to "native code", i.e. machine code for the target
microcontroller (such as ARM Thumb, Xtensa, x86/x64). The ``@native``
decorator can be applied to a MicroPython function to generate native
code instead of :term:`bytecode` for that function, which will likely be
faster but use more RAM.
port
Usually short for :term:`MicroPython port`, but could also refer to
:term:`GPIO port`.
.py file
A file containing Python source code.
REPL
An acronym for "Read, Eval, Print, Loop". This is the interactive
Python prompt, useful for debugging or testing short snippets of code.
Most MicroPython boards make a REPL available over a UART, and this is
typically accessible on a host PC via USB.
stream
Also known as a "file-like object". A Python object which provides
sequential read-write access to the underlying data. A stream object
implements a corresponding interface, which consists of methods like
``read()``, ``write()``, ``readinto()``, ``seek()``, ``flush()``,
``close()``, etc. A stream is an important concept in MicroPython;
many I/O objects implement the stream interface, and thus can be used
consistently and interchangeably in different contexts. For more
information on streams in MicroPython, see the `io` module.
UART
Acronym for "Universal Asynchronous Receiver/Transmitter". This is a
peripheral that sends data over a pair of pins (TX & RX). Many boards
include a way to make at least one of the UARTs available to a host PC
as a serial port over USB.
upip
A now-obsolete package manager for MicroPython, inspired
by :term:`CPython`'s pip, but much smaller and with reduced
functionality. See its replacement, :term:`mip`.
webrepl
A way of connecting to the REPL (and transferring files) on a device
over the internet from a browser. See https://micropython.org/webrepl