Glossary
========
.. glossary::
baremetal
A system without a (full-fledged) OS, for example an
:term:`MCU`-based system. When running on a baremetal system,
MicroPython effectively becomes its user-facing OS with a command
interpreter (REPL).
board
A PCB board. Oftentimes, the term is used to denote a particular
model of an :term:`MCU` system. Sometimes, it is used to actually
refer to :term:`MicroPython port` to a particular board (and then
may also refer to "boardless" ports like
:term:`Unix port <MicroPython Unix port>`).
callee-owned tuple
A tuple returned by some builtin function/method, containing data
which is valid for a limited time, usually until next call to the
same function (or a group of related functions). After next call,
data in the tuple may be changed. This leads to the following
restriction on the usage of callee-owned tuples - references to
them cannot be stored. The only valid operation is extracting
values from them (including making a copy). Callee-owned tuples
is a MicroPython-specific construct (not available in the general
Python language), introduced for memory allocation optimization.
The idea is that callee-owned tuple is allocated once and stored
on the callee side. Subsequent calls don't require allocation,
allowing to return multiple values when allocation is not possible
(e.g. in interrupt context) or not desirable (because allocation
inherently leads to memory fragmentation). Note that callee-owned
tuples are effectively mutable tuples, making an exception to
Python's rule that tuples are immutable. (It may be interesting
why tuples were used for such a purpose then, instead of mutable
lists - the reason for that is that lists are mutable from user
application side too, so a user could do things to a callee-owned
list which the callee doesn't expect and could lead to problems;
a tuple is protected from this.)
CPython
CPython is the reference implementation of Python programming
language, and the most well-known one, which most of the people
run. It is however one of many implementations (among which
Jython, IronPython, PyPy, and many more, including MicroPython).
As there is no formal specification of the Python language, only
CPython documentation, it is not always easy to draw a line
between Python the language and CPython its particular
implementation. This however leaves more freedom for other
implementations. For example, MicroPython does a lot of things
differently than CPython, while still aspiring to be a Python
language implementation.
GPIO
General-purpose input/output. The simplest means to control
electrical signals. With GPIO, user can configure hardware
signal pin to be either input or output, and set or get
its digital signal value (logical "0" or "1"). MicroPython
abstracts GPIO access using :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).
interned string
A string referenced by its (unique) identity rather than its
address. Interned strings are thus can be quickly compared just
by their identifiers, instead of comparing by content. The
drawbacks of interned strings are that interning operation takes
time (proportional to the number of existing interned strings,
i.e. becoming slower and slower over time) and that the space
used for interned strings is not reclaimable. String interning
is done automatically by MicroPython compiler and runtimer when
it's either required by the implementation (e.g. function keyword
arguments are represented by interned string id's) or deemed
beneficial (e.g. for short enough strings, which have a chance
to be repeated, and thus interning them would save memory on
copies). Most of string and I/O operations don't produce interned
strings due to drawbacks described above.
MCU
Microcontroller. Microcontrollers usually have much less resources
than a full-fledged computing system, but 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`. 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. However, large subset of these modules require
POSIX-like environment (Linux, FreeBSD, MacOS, etc.; Windows may be
partially supported), and thus would work or make sense only with
`MicroPython Unix port`. Some subset of modules is however usable
for `baremetal` ports too.
Unlike monolithic :term:`CPython` stdlib, micropython-lib modules
are intended to be installed individually - either using manual
copying or using :term:`upip`.
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 MicroPython core functionality,
would be described in the separate port-specific documentation.
MicroPython Unix port
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 importance of Unix port lies in the fact
that while there are many different :term:`boards <board>`, so
two random users unlikely have the same board, almost all modern
OSes have some level of POSIX compatibility, so Unix port serves
as a kind of "common ground" to which any user can have access.
So, Unix port is used for initial prototyping, different kinds
of testing, development of machine-independent features, etc.
All users of MicroPython, even those which are interested only
in running MicroPython on :term:`MCU` systems, are recommended
to be familiar with Unix (or Windows) port, as it is important
productivity helper and a part of normal MicroPython workflow.
port
Either :term:`MicroPython port` or :term:`GPIO port`. If not clear
from context, it's recommended to use full specification like one
of the above.
stream
Also known as a "file-like object". An 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 `uio` module.
upip
(Literally, "micro pip"). A package manage for MicroPython, inspired
by :term:`CPython`'s pip, but much smaller and with reduced functionality.
upip runs both on :term:`Unix port <MicroPython Unix port>` and on
:term:`baremetal` ports (those which offer filesystem and networking
support).