[Tutor] truncated dictionary return

[richard kappler]

Now I'm completely lost. While opening the serial port outside the function
sounds like a good idea, I'm thinking that might not work unless I am
mistaken. The sensorRead function once it's called would then basically own
the serial port barring other traffic, yes? That won't work as the same
serial port that receives sensor data from the arduino sends propulsion and
nav signals to the arduino which, along with controlling/reading the
sensors, also controls the motors used for propulsion, hence only opening
the port when the data is called for. The sensorRead function works, heck
it's not even mine, it was written by one of the gurus here in response to
a question I posed months ago (either Alan or Eryksun IIRC) and does
exactly what it's supposed to do, except for the timing bit.

Perhaps I'm looking for a simple solution where none exists but I rather
doubt it. I was thinking something along the lines of (psuedo code here)
check incoming dict for length or number of elements
if 8, keep
else retry

While I appreciate the above comments and any help that is offered, I
neither understand them as presented nor think they will fix the problem
with the limited understanding I do have. Again, it could be my lack of
knowledge is preventing me from seeing the light here, but it feels like
we're reinventing the wheel.

I hope that didn't come across as rude, it truly was not intended to be
such.

regards, Richard


On Sun, Dec 1, 2013 at 3:06 PM, spir <denis.spir at gmail.com> wrote:

> On 12/01/2013 08:28 PM, richard kappler wrote:
>
>> I have a script that reads sensor values gathered by an Arduino board from
>> serial as a dictionary, said values to later be used in the AI for Nav &
>> Control. Here's the script:
>>
>> #!/usr/bin/python
>>
>> def sensorRead():
>>      import serial
>>      from time import sleep
>>
>>      sensors = {}
>>      sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
>> Temperature Humidity Light'.split())
>>
>>      arduino = serial.Serial('/dev/ttyACM0', 9600)
>>      sleep(1)
>>      line = arduino.readline().strip()
>>      line = line.lstrip('{').rstrip('}').strip()
>>
>>      d = {}
>>      for item in line.split(','):
>>          item = item.strip()
>>          key, value = item.split(':')
>>          key = key.strip()
>>          value = value.strip()
>>          d[key]=int(value)
>>      return d
>>
>> I hope that comes through okay, I copied it from the text file so
>> indentation and such should be fine, if not let me know.
>>
>> The script works great with one exception. I understand the problem, I'm
>> just not sure how to address it. The problem is:
>>
>> The Arduino runs on a constant loop, it reads each sensor, sends the key
>> and the value to the serial bus in format for python to read it as a
>> dictionary, lather, rinse, repeat.
>>
>> Python querries the bus when told. Usually the python script gets the full
>> dictionary (all 8 values with keys, brackets etc) but sometimes it
>> doesn't.
>> Sometimes it only gets the last few values, sometimes it gets nothing or
>> misses a bracket and throws an error. This makes sense. They are not in
>> sync.
>>
>> What I need to figure out how to do is have the python script wait until
>> the next round of values as signified by the opening bracket "{" or check
>> that it has all 8 values and if not retry or.... something.
>>
>> Would this be an if/else? try? exception?
>>
>> I've not yet delved into any of these in my quest to learn python except
>> if/else and that doesn't feel right for this, so I'm at a loss as to how
>> to
>> proceed.
>>
>
> * What is the point of the 'sensors' dict? (also, you don't need to
> initialise it as an enmpty dict)
> * If you know about regexps or another matching utility, use that to
> decode the input line into (key,value) pairs. This is even easier if input
> has a strict format. Would tell us?
> * About wrong input (incomplete data), avoid try/except, except if ever
> most cases are ok (it is very costly in case of exception). Anyway, you
> need to decode input, so use that to check for errors/missing stuff.
>
> If you used a matching tool, its absence of result would directly tell
> about wrong input (provided your pattern is correct! ;-) As of now, just
> place checks in your decoding sequence. Possible checks places, at first
> sight, marked below:
>
>
>     line = arduino.readline().strip()
>     line = line.lstrip('{').rstrip('}').strip()
>     # check line not empty
>     # (actually big enough for at least {} + one key:val entry)
>
>     d = {}
>     # first get items in separate var and check how many:
>
>     for item in line.split(','):
>         item = item.strip()          # not needed, for you strip key/val
> again later
>         # first get tuple from split() and check its size is 2
>
>         key, value = item.split(':')
>         key = key.strip()
>         value = value.strip()        # not needed, for int() itself strips
>         # maybe one try/except here for checking conversion to int:
>         # (else, you need to check yourself it is an int numeral)
>         d[key]=int(value)
>
> Each check failure is a sign of wrong input. What do you need to do, then?
> Abandon the whole round?
>
> Denis
>
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