Python keyboard input for teleop [user interface]

I recently ask myself how to implement the user interface of the teleop program of my robot. This is the first version, the most basic and the most straightforward one, so the user interface will be based on keyboard inputs. This teleop program is written in Python. The user will have to input some information to trigger an action on the robot.

In a console based program, the user input in Pyhton is usually done by the input() function. If this one is perfect for a single data input, the user experience will be really poor in case of a teleop program.

An obvious idea would be to wait for a key press, which is commonly done for such a program. This kind of feature is deeply related to the OS, and means a lot of code for a perfect portability (see this question on Stackoverflow). Of course I could only implement the code for Linux. Another drawback is that the arrow keys are not well supported (because they are a set of three keys), and the arrow keys are an obvious choice for commanding a mobile base.

This can be improved with additional libraries dealing with “events” management. An event is a background process, listening for an action from the user, like a key press or mouse movement. The module curses, for example, implements ncurses functions in Python. An even better option could be pygame. This module is designed for developing multimedia games in Python. The last one makes sense, since controlling a robot may be not that far from the interaction you expect from a video game.

The keyboard input management does not come alone in such modules. You need to call the whole graphical user interface (GUI) provided by those modules. Pygame, for example, need a graphic window to work properly. So for handling the keyboard inputs, that looks too heavy and finally not clean. Moreover, that looks far from the spirit of a console program.

Finally I discovered the cmd module. This module provides a command line object, easy to implement and very well integrated with the Python code. Here is a short list of features:

• Automatic parse the user input (the first word is used to call a routine previously defined)
• Pre-defined “help” command, listing all defined commands and even display help text based on docstring
• Navigation through the history of previously entered commands

You can read this blog post for a full description of the features of this module, and the Python docs.

This module is the perfect option for repetitive entries of command lines, what you typically do when you teleop a robot. The final result looks like this screenshot:

Python keyboard input using cmd applied to a teleop program

Moreover, the online help is very convenient for the deployment of the application in the next steps. To achieve this result, I had to have a fresh look at the user interaction in console mode and try to find a solution in the spirit of Python. After a couple of days, I confirm that I’m really satisfied by this option.

A key being pressed on a computer keyboard (source Wikipedia)

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