[Tutor] Pen plotter data format

[Dennis Lee Bieber]

On Sat, 01 Apr 2023 02:20:09 -0400, Dennis Lee Bieber
<wlfraed at ix.netcom.com> declaimed the following:


>while True:
>	command_string = serial.readline()		#block for EOL
>	commands = command_string.split(";")	#split into each command
>	for command in commands:				#process each command
>		cmd, parameters = command[:2], command[2:]
>		#call the handler function matching "cmd"
>		#all handlers have the same signature!
>		result = command_table[cmd.upper()](parameters)
>		if not result:
>			serial.write("%s : %s\n" % (command, result))
>
>Adding a command just requires adding a new "def cmd_handler()" and an
>entry in the command_table.
>

	I need to state that, the above "parser" will fail if you've added plot
commands for text printing -- as an embedded ";" will cause a split in the
wrong location. For that situation you'll need a stream parsing approach.
Hypothetical command format (Text Output): TO<len>,<some amount of text>

Something similar to:

while True:
	command_string = serial.readline()
	while command_string:
		cmd, command_string = (command_string[:2].upper(),
									command_string[2:])
		if cmd in [ "TO", <other similar format commands>]:
			len, command_string = command_string.split(",", 1)
			ilen = int(len)
			parameters, command_string = (command_string[:ilen],
											command_string[ilen+1:])
					#^^^ skips ";" separator
					#vvv recreate "signature" for calling handlers
			parameters = ",".join([len, parameters])
		else:
			parameters, command_string = command_string.split(";", 1)
		result = command_table[cmd](parameters)



And... before I forget... Adafruit's "blinka" package enables using most of
the CircuitPython interfaces from a Python running on R-Pi (or BeagleBone
Black -- the BB AI is overkill for this). But given the rarity and rising
$$$ for R-Pis I'd recommend using a controller board over a computer board
-- again the Metro Express seems suited if one wants to stay in Python.