Storing Value in Arduino Sent From Python via Serial - python-3.x

Question

I have been trying to send a value from a Python program via serial to an Arduino, but I have been unable to get the Arduino to store and echo back the value to Python. My code seems to match that I've found in examples online, but for whatever reason, it's not working.
I am using Python 3.5 on Windows 10 with an Arduino Uno. Any help would be appreciated.
Arduino code:
void readFromPython() {
if (Serial.available() > 0) {
incomingIntegrationTime = Serial.parseInt();
// Collect the incoming integer from PySerial
integration_time = incomingIntegrationTime;
Serial.print("X");
Serial.print("The integration time is now ");
// read the incoming integer from Python:
// Set the integration time to what you just collected IF it is not a zero
Serial.println(integration_time);
Serial.print("\n");
integration_time=min(incomingIntegrationTime,2147483648);
// Ensure the integration time isn't outside the range of integers
integration_time=max(incomingIntegrationTime, 1);
// Ensure the integration time isn't outside the range of integers
}
}
void loop() {
readFromPython();
// Check for incoming data from PySerial
delay(1);
// Pause the program for 1 millisecond
}
Python code:
(Note this is used with a PyQt button, but any value could be typed in instead of self.IntegrationTimeInputTextbox.text() and the value is still not receieved and echoed back by Arduino).
def SetIntegrationTime(self):
def main():
# global startMarker, endMarker
#This sets the com port in PySerial to the port with the Genuino as the variable arduino_ports
arduino_ports = [
p.device
for p in serial.tools.list_ports.comports()
if 'Genuino' in p.description
]
#Set the proper baud rate for your spectrometer
baud = 115200
#This prints out the port that was found with the Genuino on it
ports = list(serial.tools.list_ports.comports())
for p in ports:
print ('Device is connected to: ', p)
# --------------------------- Error Handling ---------------------------
#Tell the user if no Genuino was found
if not arduino_ports:
raise IOError("No Arduino found")
#Tell the user if multiple Genuinos were found
if len(arduino_ports) > 1:
warnings.warn('Multiple Arduinos found - using the first')
# ---------------------------- Error Handling ---------------------------
#=====================================
spectrometer = serial.Serial(arduino_ports[0], baud)
integrationTimeSend = self.IntegrationTimeInputTextbox.text()
print("test value is", integrationTimeSend.encode())
spectrometer.write(integrationTimeSend.encode())
for i in range(10): #Repeat the following 10 times
startMarker = "X"
xDecoded = "qq"
xEncoded = "qq"
while xDecoded != startMarker: #Wait for the start marker (X))
xEncoded = spectrometer.read() #Read the spectrometer until 'startMarker' is found so the right amound of data is read every time
xDecoded = xEncoded.decode("UTF-8");
print(xDecoded);
line = spectrometer.readline()
lineDecoded = line.decode("UTF-8")
print(lineDecoded)
#=====================================
spectrometer.close()
#===========================================
#WaitForArduinoData()
main()

Answer 1

First, this is a problem:
incomingValue = Serial.read();
Because read() returns the first byte of incoming serial data reference. On the Arduino the int is a signed 16-bit integer, so reading only one byte of it with a Serial.read() is going to give you unintended results.
Also, don't put writes in between checking if data is available and actual reading:
if (Serial.available() > 0) {
Serial.print("X"); // Print your startmarker
Serial.print("The value is now ");
incomingValue = Serial.read(); // Collect the incoming value from
That is bad. Instead do your read immediately as this example shows:
if (Serial.available() > 0) {
// read the incoming byte:
incomingByte = Serial.read();
That's two big issues there. Take care of those and let's take a look at it after those fundamental issues are corrected.
PART 2
Once those are corrected, the next thing to do is determine which side of the serial communication is faulty. Generally what I like to do is determine one side is sending properly by having its output show up in a terminal emulator. I like TeraTerm for this.
Set your python code to send only and see if your sent values show up properly in a terminal emulator. Once that is working and you have confidence in it, you can attend to the Arduino side.