title: Trouble sending data from Matlab to Python via serial port
body: <p>to better understand serial port communication, I am trying to write some sample code, where Matlab has a loop running, which continously sends data to a serial port, while a Python script running on the same windows machine listens to this port, then receives and prints any received data.</p>
  
  <p>In Matlab, I have written a simple loop, which sends 99 test signals to Port COM1, </p>
  
  <pre><code>% Setup a serial port and open it
  tep=serial("COM1", "Baudrate", 9600);
  fopen(tep);
  
  % this loop is supposed to send a number to a serial port repeatedly
  n = 1; % counter variable
  while n &lt; 100
      fprintf(tep,"50"); % Send data to serial port
      n = n + 1;      % Counter variable
      pause(0.5)      % Sleep to make this loop run for a total of 50s0
      fprintf('run'); % Test output within matlab to check, whether it runs
  end
  
  % finally close the serial port
  fclose(tep);
  </code></pre>
  
  <p>as far as I can tell, this Matlab part works, as it prints "run" every hald second. </p>
  
  <p>The Python listener:</p>
  
  <pre><code>import serial
  import time
  # set up the serial line same as in Matlab
  ser = serial.Serial('COM1', 9600)
  time.sleep(2)
  
  # Read and record the data
  data =[]                       # empty list to store the data
  for i in range(50):
      b = ser.readline()         # read a byte string
      string_n = b.decode()  # decode byte string into Unicode  
      string = string_n.rstrip() # remove \n and \r
      flt = float(string)        # convert string to float
      print(flt)
      data.append(flt)           # add to the end of data list
      time.sleep(0.1)            # wait (sleep) 0.1 seconds
  
  ser.close()
  
  # show the data
  
  for line in data:
      print(line)
  </code></pre>
  
  <p>Running the script in Python results in the following error: </p>
  
  <pre><code>serial.serialutil.SerialException: could not open port 'COM1': PermissionError(13, 'Zugriff verweigert', None, 5)
  </code></pre>
  
  <p>Obviously the port is already in use by Matlab, as it sends information to it, but I don't understand, why that is a problem. Shouldn't it be fine, for one program to send data to it and for another to receive data from it?</p>
  
  <p>Kind regards.</p>