PythonExtra libraries

Warning

Important summary of this section

• PythonExtra provides built-in modules that mirror the functionality of the Python standard library (e.g. os, time), as well as PythonExtra-specific modules (e.g. bluetooth, machine).

• Most Python standard library modules implement a subset of the functionality of the equivalent Python module, and in a few cases provide some PythonExtra-specific extensions (e.g. array, os)

• Due to resource constraints or other limitations, some ports or firmware versions may not include all the functionality documented here.

• To allow for extensibility, some built-in modules can be extended from Python code loaded onto the device filesystem.

This chapter describes modules (function and class libraries) which are built into PythonExtra. This documentation in general aspires to describe all modules and functions/classes which are implemented in the PythonExtra project. However, PythonExtra is highly configurable, and each port to a particular board/embedded system may include only a subset of the available PythonExtra libraries.

With that in mind, please be warned that some functions/classes in a module (or even the entire module) described in this documentation may be unavailable in a particular build of PythonExtra on a particular system. The best place to find general information of the availability/non-availability of a particular feature is the “General Information” section which contains information pertaining to a specific PythonExtra port.

On some ports you are able to discover the available, built-in libraries that can be imported by entering the following at the REPL:

help('modules')

Beyond the built-in libraries described in this documentation, many more modules from the Python standard library, as well as further PythonExtra extensions to it, can be found in micropython-lib.

Python standard libraries and micro-libraries

The following standard Python libraries have been “micro-ified” to fit in with the philosophy of PythonExtra. They provide the core functionality of that module and are intended to be a drop-in replacement for the standard Python library.

• array – arrays of numeric data
• builtins – builtin functions and exceptions
• cmath – mathematical functions for complex numbers
• collections – collection and container types
• gc – control the garbage collector
• gint — CASIO calculator hardware access
• io – input/output streams
• marshal – Python object serialization
• math – mathematical functions
• os – basic “operating system” services
• platform – access to underlying platform’s identifying data
• random – generate random numbers
• struct – pack and unpack primitive data types
• sys – system specific functions
• time – time related functions

PythonExtra-specific libraries

Functionality specific to the PythonExtra implementation is available in the following libraries.

• machine — functions related to the hardware
• micropython – access and control PythonExtra internals
• uctypes – access binary data in a structured way
• vfs – virtual filesystem control

Port-specific libraries

In some cases the following port/board-specific libraries have functions or classes similar to those in the machine library. Where this occurs, the entry in the port specific library exposes hardware functionality unique to that platform.

To write portable code use functions and classes from the machine module. To access platform-specific hardware use the appropriate library, e.g. pyb in the case of the Pyboard.

Libraries specific to the ClassPad

The following libraries are specific to the pyboard.

• casioplot — simplified graphics plotting
  • Functions
• gint — CASIO calculator hardware access
  • Classes
  • Functions
  • Constants

Extending built-in libraries from Python

A subset of the built-in modules are able to be extended by Python code by providing a module of the same name in the filesystem. This extensibility applies to the following Python standard library modules which are built-in to the firmware: array, binascii, collections, errno, gzip, hashlib, heapq, io, json, os, platform, random, re, select, socket, ssl, struct, time zlib, as well as the PythonExtra-specific machine module. All other built-in modules cannot be extended from the filesystem.

This allows the user to provide an extended implementation of a built-in library (perhaps to provide additional CPython compatibility or missing functionality). This is used extensively in micropython-lib, see Package management for more information. The filesystem module will typically do a wildcard import of the built-in module in order to inherit all the globals (classes, functions and variables) from the built-in.

In PythonExtra v1.21.0 and higher, to prevent the filesystem module from importing itself, it can force an import of the built-in module it by temporarily clearing sys.path during the import. For example, to extend the time module from Python, a file named time.py on the filesystem would do the following:

_path = sys.path
sys.path = ()
try:
  from time import *
finally:
  sys.path = _path
  del _path

def extra_method():
  pass

The result is that time.py contains all the globals of the built-in time module, but adds extra_method.

In earlier versions of PythonExtra, you can force an import of a built-in module by appending a u to the start of its name. For example, import utime instead of import time. For example, time.py on the filesystem could look like:

from utime import *

def extra_method():
  pass

This way is still supported, but the sys.path method described above is now preferred as the u-prefix will be removed from the names of built-in modules in a future version of PythonExtra.

Other than when it specifically needs to force the use of the built-in module, code should always use import module rather than import umodule.