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.

import ev3dev.ev3 as ev3

import ev3dev.brickpi as ev3

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

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

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

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 Robot

Laurens Valk of robot-square has been kind enough to allow us to reference his excellent EXPLOR3R robot. Consider building the EXPLOR3R and running the demo programs referenced below to get familiar with what Python programs using this binding look like.

Demo Code

There are demo programs that you can run to get acquainted with this language binding. The programs are designed to work with the EXPLOR3R robot.

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

API reference¶

Each class in ev3dev module inherits from the base Device class.

Contents:

Motor classes¶

Tacho motor¶

Large EV3 Motor¶

Medium EV3 Motor¶

DC Motor¶

Servo Motor¶

Sensor classes¶

Sensor¶

This is the base class all the other sensor classes are derived from.

Special sensor classes¶

The classes derive from Sensor and provide helper functions specific to the corresponding sensor type. Each of the functions makes sure the sensor is in the required mode and then returns the specified value.

Touch Sensor¶

Color Sensor¶

Ultrasonic Sensor¶

Gyro Sensor¶

Infrared Sensor¶

Sound Sensor¶

Light Sensor¶

Other classes¶

Remote Control¶

Beacon Seeker¶

Button¶

Leds¶

Power Supply¶

Sound¶

Screen¶

Bitmap fonts¶

The Screen class allows to write text on the LCD using python imaging library (PIL) interface (see description of the text() method here). The ev3dev.fonts module contains bitmap fonts in PIL format that should look good on a tiny EV3 screen:

import ev3dev.fonts as fonts
screen.draw.text((10,10), 'Hello World!', font=fonts.load('luBS14'))

ev3dev.fonts.available()¶

Returns list of available font names.

ev3dev.fonts.load(name)¶

Loads the font specified by name and returns it as an instance of PIL.ImageFont class.

The following image lists all available fonts. The grid lines correspond to EV3 screen size:

Lego Port¶

Working with ev3dev remotely using RPyC¶

RPyC (pronounced as are-pie-see), or Remote Python Call, is a transparent python library for symmetrical remote procedure calls, clustering and distributed-computing. RPyC makes use of object-proxying, a technique that employs python’s dynamic nature, to overcome the physical boundaries between processes and computers, so that remote objects can be manipulated as if they were local. Here are simple steps you need to follow in order to install and use RPyC with ev3dev:

1. Install RPyC both on the EV3 and on your desktop PC. For the EV3, enter the following command at the command prompt (after you connect with SSH):

   sudo easy_install3 rpyc
   

   On the desktop PC, it really depends on your operating system. In case it is some flavor of linux, you should be able to do

   sudo pip3 install rpyc
   

   In case it is Windows, there is a win32 installer on the project’s sourceforge page. Also, have a look at the Download and Install page on their site.

2. Create file rpyc_server.sh with the following contents on the EV3:

   #!/bin/bash
   python3 `which rpyc_classic.py`
   

   and make the file executable:

   chmod +x rpyc_server.sh
   

   Launch the created file either from SSH session (with ./rpyc_server.sh command), or from brickman. It should output something like

   INFO:SLAVE/18812:server started on [0.0.0.0]:18812
   

   and keep running.

3. Now you are ready to connect to the RPyC server from your desktop PC. The following python script should make a large motor connected to output port A spin for a second.

   import rpyc
   conn = rpyc.classic.connect('ev3dev') # host name or IP address of the EV3
   ev3 = conn.modules['ev3dev.ev3']      # import ev3dev.ev3 remotely
   m = ev3.LargeMotor('outA')
   m.run_timed(time_sp=1000, speed_sp=600)
   

You can run scripts like this from any interactive python environment, like ipython shell/notebook, spyder, pycharm, etc.

Some advantages of using RPyC with ev3dev are:

• It uses much less resources than running ipython notebook on EV3; RPyC server is lightweight, and only requires an IP connection to the EV3 once set up (no ssh required).
• The scripts you are working with are actually stored and edited on your desktop PC, with your favorite editor/IDE.
• Some robots may need much more computational power than what EV3 can give you. A notable example is the Rubics cube solver: there is an algorithm that provides almost optimal solution (in terms of number of cube rotations), but it takes more RAM than is available on EV3. With RPYC, you could run the heavy-duty computations on your desktop.

The most obvious disadvantage is latency introduced by network connection. This may be a show stopper for robots where reaction speed is essential.

Frequently-Asked Questions¶

My script works when launched as python3 script.py but exits immediately or throws an error when launched from Brickman or as ./script.py¶

This may occur if your file includes Windows-style line endings, which are often inserted by editors on Windows. To resolve this issue, open an SSH session and run the following command, replacing <file> with the name of the Python file you’re using:

sed -i 's/\r//g' <file>

This will fix it for the copy of the file on the brick, but if you plan to edit it again from Windows you should configure your editor to use Unix-style endings. For PyCharm, you can find a guide on doing this here. Most other editors have similar options; there may be an option for it in the status bar at the bottom of the window or in the menu bar at the top.