Python language bindings for ev3dev

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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 can certainly use this library to help you learn the language!

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 you have an ev3dev-stretch version greater than 2.2.0. 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.

Usage

To start out, you'll need a way to work with Python. We recommend the ev3dev Visual Studio Code extension. If you're interested in using that, check out our Python + VSCode introduction tutorial and then come back once you have that set up.

Otherwise, you can can work with files via an SSH connection_ with an editor such as nano_, use the Python interactive REPL (type python3), or roll your own solution. If you don't know how to do that, you are probably better off choosing the recommended option above.

The template for a Python script

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

.. code-block:: python

   #!/usr/bin/env python3
   
   from time import sleep
   
   from ev3dev2.motor import LargeMotor, OUTPUT_A, OUTPUT_B, SpeedPercent, MoveTank
   from ev3dev2.sensor import INPUT_1
   from ev3dev2.sensor.lego import TouchSensor
   from ev3dev2.led import Leds

   # TODO: Add code here

The first line should be included in every Python program you write
for ev3dev. It allows you to run this program from Brickman, the graphical
menu that you see on the device screen. The other lines are import statements
which give you access to the library functionality. You will need to add
additional classes to the import list if you want to use other types of devices
or additional utilities.

You should use the ``.py`` extension for your file, e.g. ``my-file.py``.

If you encounter an error such as
``/usr/bin/env: 'python3\r': No such file or directory``,
you must switch your editor's "line endings" setting for the file from
"CRLF" to just "LF". This is usually in the status bar at the bottom.
For help, see `our FAQ page`_.

Important: Make your script executable (non-Visual Studio Code only)

To be able to run your Python file, your program must be executable. If you are using the ev3dev Visual Studio Code extension_, you can skip this step, as it will be automatically performed when you download your code to the brick.

To mark a program as executable from the command line (often an SSH session), run chmod +x my-file.py.

You can now run my-file.py via the Brickman File Browser or you can run it from the command line by preceding the file name with ./: ./my-file.py

Controlling the LEDs with a touch sensor

This code will turn the LEDs red whenever the touch sensor is pressed, and
back to green when it's released. Plug a touch sensor into any sensor port
before trying this out.

.. code-block:: python

  ts = TouchSensor()
  leds = Leds()

  print("Press the touch sensor to change the LED color!")

  while True:
      if ts.is_pressed:
          leds.set_color("LEFT", "GREEN")
          leds.set_color("RIGHT", "GREEN")
      else:
          leds.set_color("LEFT", "RED")
          leds.set_color("RIGHT", "RED")
      # don't let this loop use 100% CPU
      sleep(0.01)

If you'd like to use a sensor on a specific port, specify the port like this:

.. code-block:: python

  ts = TouchSensor(INPUT_1)

*Heads-up:* If you are using a BrickPi instead of an EV3, you will need to manually configure the sensor. See the example here: https://github.com/ev3dev/ev3dev-lang-python-demo/blob/stretch/platform/brickpi3-motor-and-sensor.py

Running a single motor
~~~~~~~~~~~~~~~~~~~~~~

This will run a LEGO Large Motor at 75% of maximum speed for 5 rotations.

.. code-block:: python

  m = LargeMotor(OUTPUT_A)
  m.on_for_rotations(SpeedPercent(75), 5)

You can also run a motor for a number of degrees, an amount of time, or simply
start it and let it run until you tell it to stop. Additionally, other units
are also available. See the following pages for more information:

- http://python-ev3dev.readthedocs.io/en/ev3dev-stretch/motors.html#ev3dev.motor.Motor.on_for_degrees
- http://python-ev3dev.readthedocs.io/en/ev3dev-stretch/motors.html#units

Driving with two motors
~~~~~~~~~~~~~~~~~~~~~~~

The simplest drive control style is with the `MoveTank` class:

.. code-block:: python

    tank_drive = MoveTank(OUTPUT_A, OUTPUT_B)

    # drive in a turn for 5 rotations of the outer motor
    # the first two parameters can be unit classes or percentages.
    tank_drive.on_for_rotations(SpeedPercent(50), SpeedPercent(75), 10)

    # drive in a different turn for 3 seconds
    tank_drive.on_for_seconds(SpeedPercent(60), SpeedPercent(30), 3)

There are also `MoveSteering` and `MoveJoystick` classes which provide
different styles of control. See the following pages for more information:

- http://python-ev3dev.readthedocs.io/en/ev3dev-stretch/motors.html#multiple-motor-groups
- http://python-ev3dev.readthedocs.io/en/ev3dev-stretch/motors.html#units

Using text-to-speech
~~~~~~~~~~~~~~~~~~~~

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

.. code-block:: python

  from ev3dev2.sound import Sound

  sound = Sound()
  sound.speak('Welcome to the E V 3 dev project!')

More Demo Code
~~~~~~~~~~~~~~

There are several demo programs that you can run to get acquainted with
this language binding. The programs are available
`at this GitHub site <https://github.com/ev3dev/ev3dev-lang-python-demo>`_.

You can also copy and run the programs in the `utils` directory to
understand some of the code constructs to use the EV3 motors, sensors,
LCD console, buttons, sound, and LEDs.

We also highly recommend `ev3python.com`_ where 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`_!

Using Micropython
-----------------

Normal Python too slow? Review `Micropython`_ to see if it supports the
features your project needs.

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.


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: http://ev3dev.org
.. _ev3dev.org: ev3dev_
.. _Getting Started: ev3dev-getting-started_
.. _ev3dev Getting Started guide: ev3dev-getting-started_
.. _ev3dev-getting-started: http://www.ev3dev.org/docs/getting-started/
.. _upgrade the kernel before continuing: http://www.ev3dev.org/docs/tutorials/upgrading-ev3dev/
.. _detailed instructions for USB connections: ev3dev-usb-internet_
.. _via an SSH connection: http://www.ev3dev.org/docs/tutorials/connecting-to-ev3dev-with-ssh/
.. _ev3dev-usb-internet: http://www.ev3dev.org/docs/tutorials/connecting-to-the-internet-via-usb/
.. _our Read the Docs page: http://python-ev3dev.readthedocs.org/en/ev3dev-stretch/
.. _ev3python.com: http://ev3python.com/
.. _FAQ: http://python-ev3dev.readthedocs.io/en/ev3dev-stretch/faq.html
.. _our FAQ page: FAQ_
.. _our Issues tracker: https://github.com/ev3dev/ev3dev-lang-python/issues
.. _EXPLOR3R: demo-robot_
.. _demo-robot: http://robotsquare.com/2015/10/06/explor3r-building-instructions/
.. _robot-square: http://robotsquare.com/
.. _Python 2.x: python2_
.. _python2: https://docs.python.org/2/
.. _Python 3.x: python3_
.. _python3: https://docs.python.org/3/
.. _package repository: pypi_
.. _pypi: https://pypi.python.org/pypi
.. _latest version of this package: pypi-python-ev3dev_
.. _pypi-python-ev3dev: https://pypi.python.org/pypi/python-ev3dev2
.. _ev3dev Visual Studio Code extension: https://github.com/ev3dev/vscode-ev3dev-browser
.. _Python + VSCode introduction tutorial: https://github.com/ev3dev/vscode-hello-python
.. _nano: http://www.ev3dev.org/docs/tutorials/nano-cheat-sheet/
.. _Micropython: http://python-ev3dev.readthedocs.io/en/ev3dev-stretch/micropython.html