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0. Contents
- Installing MicroPython library modules
- micropip upip alternative runs on a PC under CPython
- Overriding built in library modules
1. Installing MicroPython library modules
There are various forks of MicroPython, consequently libraries on
PyPi may or may not be compatible with official firmware.
This is resolved by official upip (and its micropip derivative). These
first search the official library. Only if no match is found do they install
from PyPi. For this and other reasons, pip and pip3 should not be used to
install MicroPython libraries. Use of upip is detailed in the
official docs.
Users of non-networked hardware such as the Pyboard 1.x can use upip with the
Unix build of MicroPython to install a library module to an arbitrary directory
on a PC, from where the files and directories can be copied to the target
hardware. upip and its dependency upip_utarfile may be found in the tools
directory of the source tree. This approach has the drawback of requiring the
Unix build, which must be built from source. This may be avoided by using
micropip.py in this repo which runs under CPython.
Alternatively libraries may be installed by copying files from the MicroPython library repository to the target device. However this requires some attention to detail where there are dependencies. Where modules are organised as Python packages the directory structure must be maintained.
1.1 Installing unofficial packages
PyPi hosts a wide variety of packages targeted at MicroPython. There is no
guarantee of their compatibility with the official MicroPython codebase and it
seems that some cannot even be downloaded by upip: e.g.
this issue
1.2 What micropip is and is not
Official upip cannot run under CPython. The purpose of micropip is to be a
straight port of upip for those who do not have access to the Unix build of
MicroPython. It aims to replicate the functinality of upip. Hence requests
for enhancements will be rejected. If upip is enhanced, I will port those
changes to micropip. Secondly, if I receive a report that micropip cannot
download a given unofficial package, I will check whether upip succceeds. If
upip also fails, either the package is faulty or there is a bug in upip.
Main README
2. micropip
This runs under Python 3.2 or above. Library and user modules are installed to the PC for transfer to the target. It is cross-platform and has been tested under Linux, Windows and OSX.
Help may be accessed with
micropip.py --help
or
python3 -m micropip --help
Example invocation line to install the copy module to a PC:
$ micropip.py install -p ~/rats micropython-copy
Contents
3. Overriding built in library modules
Some firmware builds include library modules as frozen bytecode. On occasion it may be necessary to replace such a module with an updated or modified alternative. The most RAM-efficient solution is to rebuild the firmware with the replacement implemented as frozen bytecode.
For users not wishing to recompile there is an alternative. The module search
order is defined in sys.path.
>>> import sys
>>> sys.path
['', '/flash', '/flash/lib']
The '' entry indicates that frozen modules will be found before those in the
filesystem. This may be overridden by issuing:
>>> import sys
>>> sys.path.append(sys.path.pop(0))
This has the following outcome:
>>> sys.path
['/flash', '/flash/lib', '']
Now modules in the filesystem will be compiled and executed in preference to those frozen as bytecode.