Command Parser

This module implements a simple command line processor. It is meant to be able to accept 1 or more bytes at a time, as they arrive from a serial port for example. Once a proper start and stop framing characters are seen, it returns all the arguments as a list of strings.

It is intended to be used from a main loop that is checking for serial or other command input. As bytes are recieved they are passed to this parser and once a properly formatted command is received it returns the args to the main loop caller. The client then decides what to do with the args. This module does not interpret the contents of any incoming commands. It just validates the format and breaks into list of args.

The format is:

• command starts with '$', anything else is ignored until start character is seen
• there can be one or more args, which are ascii characters, each separated by a comma with no spaces
• the command terminates with a newline '\n'. It can also tolerate a \r or combinations of \r\n or \n\r just to accomodate whatever various serial terminal programs do when you hit enter.
• everything is interpreted as ascii, if you pass a unicode character you will probably get garbage out
• it does not echo anything, that is up to client if needed
• everything outside of $...\n is ignored

A note about efficiency: it creates bytearrays during the process which are then eventually freed. If it causes a memory usage or gc problem then it can be revisited to see how to reuse a single allocated array instead of creating new ones on the fly.

The client is meant to only call process_input() and not the other methods in this class.

Usage:

import cmdparser

cp = cmdparser.CmdParser()

while (processing main loop):
    ...
    if incoming_bytes_are_available():
        incoming = get_the_incoming_bytes()
        cmdargs = cp.process_input(incoming)
        # if not None, then there is new args
        if cmdargs:
            numargs = len(cmdargs)
            process_command(cmdargs)
            ...
    ...