User interaction with chat interface

Previously I showed how to communicate between Python and the Arduino. Next we need a way for the user to interact with the Arduino, via the Python interface. The user might be a person, typing commands into a terminal, or it might be another script. Ultimately we will want to control the entire behavioral shaping process from another script, which for example will observe the subject's performance and adjust future trials accordingly.

For reading: Let's write out everything the arduino says to a text file. This way we'll have an exact record of what happened. Other programs can parse this file for the results so far.

For writing: This was a little more difficult. I wanted a general interface that could be used by a human or another script to communicate with the Python chatting script. I decided to use a named pipe, which is similar to a file. Anything that is written to this file-like object will be picked up by the chatting script and communicated to the Arduino, line by line.

Here's the old code as well as the new code:

The syntax for reading from the pipe is a little clunky. I wanted it to be non-blocking, because otherwise the program halts if there is nothing to read. But the non-blocking read will raise an error whenever no data is found. So we catch that exception and ignore it.

To create the pipe named TO_DEV, we just need to run:
    os.mkfifo('TO_DEV')

Now you can write to the pipe, either from another terminal like so:
    echo "MESSAGE" > TO_DEV
This automatically appends a newline.

Or from another Python script:
    pipeout = os.open('TO_DEV', os.O_WRONLY)
    os.write(pipeout, 'MESSAGE\n')
Here you have to add your own newline.


Next time I'll package this up into a complete script and demonstrate it.