Python language bindings for ev3dev

https://travis-ci.org/rhempel/ev3dev-lang-python.svg?branch=master Documentation Status

A Python3 library implementing an interface for ev3dev devices, letting you control motors, sensors, hardware buttons, LCD displays and more from Python code.

If you haven’t written code in Python before, you’ll need to learn the language before you can use this library.

Getting Started

This library runs on ev3dev. Before continuing, make sure that you have set up your EV3 or other ev3dev device as explained in the ev3dev Getting Started guide. Make sure that you have a kernel version that includes -10-ev3dev or higher (a larger number). You can check the kernel version by selecting “About” in Brickman and scrolling down to the “kernel version”. If you don’t have a compatible version, upgrade the kernel before continuing. Also note that if the ev3dev image you downloaded was created before September 2016, you probably don’t have the most recent version of this library installed: see Upgrading this Library to upgrade it.

Once you have booted ev3dev and connected to your EV3 (or Raspberry Pi / BeagleBone) via SSH, you should be ready to start using ev3dev with Python: this library is included out-of-the-box. If you want to go through some basic usage examples, check out the Usage Examples section to try out motors, sensors and LEDs. Then look at Writing Python Programs for Ev3dev to see how you can save your Python code to a file.

Make sure that you look at the User Resources section as well for links to documentation and larger examples.

Usage Examples

To run these minimal examples, run the Python3 interpreter from the terminal using the python3 command:

$ python3
Python 3.4.2 (default, Oct  8 2014, 14:47:30)
[GCC 4.9.1] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

The >>> characters are the default prompt for Python. In the examples below, we have removed these characters so it’s easier to cut and paste the code into your session.

Required: Import the library

If you are using an EV3 brick (which is the case for most users), add the following to the top of your file:

import ev3dev.ev3 as ev3

If you are using a BrickPi, use this line:

import ev3dev.brickpi as ev3

Controlling the LEDs with a touch sensor

This code will turn the left LED red whenever the touch sensor is pressed, and back to green when it’s released. Plug a touch sensor into any sensor port and then paste in this code - you’ll need to hit Enter after pasting to complete the loop and start the program. Hit Ctrl-C to exit the loop.

ts = ev3.TouchSensor()
while True:
    ev3.Leds.set_color(ev3.Leds.LEFT, (ev3.Leds.GREEN, ev3.Leds.RED)[ts.value()])

Running a motor

Now plug a motor into the A port and paste this code into the Python prompt. This little program will run the motor at 500 ticks per second, which on the EV3 “large” motors equates to around 1.4 rotations per second, for three seconds (3000 milliseconds).

m = ev3.LargeMotor('outA')
m.run_timed(time_sp=3000, speed_sp=500)

The units for speed_sp that you see above are in “tacho ticks” per second. On the large EV3 motor, these equate to one tick per degree, so this is 500 degress per second.

Using text-to-speech

If you want to make your robot speak, you can use the Sound.speak method:

ev3.Sound.speak('Welcome to the E V 3 dev project!').wait()

To quit the Python REPL, just type exit() or press Ctrl-D .

Make sure to check out the User Resources section for more detailed information on these features and many others.

Writing Python Programs for Ev3dev

Every Python program should have a few basic parts. Use this template to get started:

#!/usr/bin/env python3
from ev3dev.ev3 import *

# TODO: Add code here

The first two lines should be included in every Python program you write for ev3dev. The first allows you to run this program from Brickman, while the second imports this library.

When saving Python files, it is best to use the .py extension, e.g. my-file.py. To be able to run your Python code, your program must be executable. To mark a program as executable run chmod +x my-file.py. You can then run my-file.py via the Brickman File Browser or you can run it from the command line via $ ./my-file.py

User Resources

Library Documentation
Class documentation for this library can be found on our Read the Docs page . You can always go there to get information on how you can use this library’s functionality.
ev3python.com
One of our community members, @ndward, has put together a great website with detailed guides on using this library which are targeted at beginners. If you are just getting started with programming, we highly recommend that you check it out at ev3python.com!
Frequently-Asked Questions
Experiencing an odd error or unsure of how to do something that seems simple? Check our our FAQ to see if there’s an existing answer.
ev3dev.org
ev3dev.org is a great resource for finding guides and tutorials on using ev3dev, straight from the maintainers.
Support
If you are having trouble using this library, please open an issue at our Issues tracker so that we can help you. When opening an issue, make sure to include as much information as possible about what you are trying to do and what you have tried. The issue template is in place to guide you through this process.
Demo Code
There are several demo programs that you can run to get acquainted with this language binding. The programs are available at https://github.com/ev3dev/ev3dev-lang-python-demo

Upgrading this Library

You can upgrade this library from the command line as follows. Make sure to type the password (the default is maker) when prompted.

sudo apt-get update
sudo apt-get install --only-upgrade python3-ev3dev

Developer Resources

Python Package Index
The Python language has a package repository where you can find libraries that others have written, including the latest version of this package.
The ev3dev Binding Specification
Like all of the language bindings for ev3dev supported hardware, the Python binding follows the minimal API that must be provided per this document.
The ev3dev-lang Project on GitHub
The source repository for the generic API and the scripts to automatically generate the binding. Only developers of the ev3dev-lang-python binding would normally need to access this information.

Python 2.x and Python 3.x Compatibility

Some versions of the ev3dev distribution come with both Python 2.x and Python 3.x installed but this library is compatible only with Python 3.

As of the 2016-10-17 ev3dev image, the version of this library which is included runs on Python 3 and this is the only version that will be supported from here forward.

Contents

Indices and tables