Problem when communicating Arduino and Python via CmdMessenger,

Using Arduino Programming Questions
1

I'm implementing a simply arduino project that read values from a temperature sensor and print it on Serial when the user sends the command '0;'.

In the Arduino I'm using CmdMessenger to handle the commands as snippet on the bottom of page. It seams to work, since I successful interact with it via Serial Monitor. But what I want is communicating with it via a Python programming using pySerial. So I implement the piece of code below. The program runs, but it seems it's not sending data to serial correctly.

Py main program:

from temp_read import *
dObject = Temperature('COM3')
print dObject.queryTemperature()

Py class:

import serial

class Temperature:
    def __init__(self, comPath='/dev/ttyACM0', bauds=115200):
        self.serialConnection = serial.Serial(comPath, bauds, timeout=0)

    def queryTemperature(self):
        if (not self.serialConnection.isOpen()):
            self.serialConnection.open()

        # prints True:
        print self.serialConnection.isOpen()
        self.serialConnection.write(bytes(b'0;\r'))

        while self.serialConnection.inWaiting() == 0:
            pass
        # don't reach this point. It stops on loop above
        iw = self.serialConnection.inWaiting()
        temp = (self.serialConnection.read(iw))
        return temp

Sketch

    #include <CmdMessenger.h>
    #include <OneWire.h>
    #include <DallasTemperature.h>
    
    int pinTemp = 13;
    
    CmdMessenger cmdMessenger = CmdMessenger (Serial);
    OneWire oneWire (pinTemp);
    DallasTemperature sensors (&oneWire);
    
    
    enum {
      kReadTemperature,  
      kStatus,
    };
    
    void attachCommandCallbacks (){
      cmdMessenger.attach (onUnknownCommand);
      cmdMessenger.attach (kReadTemperature, onReadTemperature);  
    }
    
    void onStatus (){
      Serial.println ("status");
      
    }
    
    void onUnknownCommand (){
      Serial.println ("unknow");
    }
    
    void onReadTemperature (){
      Serial.println ("readTemp");
      sensors.requestTemperatures();
      delay (1500);
      float temp = sensors.getTempCByIndex(0);        
      cmdMessenger.sendCmd(kStatus, (float) temp);
      
    }
    
    void setup() {
     Serial.begin(115200); 
     sensors.begin ();
     cmdMessenger.printLfCr(); 
     attachCommandCallbacks();
    }
    
    void loop() {
      cmdMessenger.feedinSerialData();
    }

UPDATE: when I run the python program in debug mode with pycharm it works.

2 
def queryTemperature(self):
        if (not self.serialConnection.isOpen()):
            self.serialConnection.open()

This may be the problem. Your PC program needs to allow for the Arduino resetting when the serial port is opened. Ideally, open the serial port when the PC program starts and leave it open until you are completely finished with the Arduino.

What Arduino are you using?

You may find some useful stuff in this Python - Arduino demo

...R

3

I'm using Arduino Uno

4

The Uno will reset when the serial port is opened on the PC.

...R