Python serial error

Question

I'm trying to get Python to read connect to an Arduino Uno on Serial port 3 so that would be COM3 in the python code. I am using Python33, The latest version on Arduino and pySerial 2.7. This is the code for the Arduino:

void setup() {
Serial.begin(9600); // set the baud rate
Serial.println("Ready"); // print "Ready" once
}
void loop() {
char inByte = ' ';
if(Serial.available()){ // only send data back if data has been sent
char inByte = Serial.read(); // read the incoming data
Serial.println(inByte); // send the data back in a new line so that it is not all one long line
}
delay(100); // delay for 1/10 of a second
}

And this is the python code:

import serial
ser = serial.Serial("COM3", 9600)

then I get this error:

Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
ser = serial.Serial("COM3", 9600)
File "C:\Python33\lib\site-packages\serial\serialwin32.py", line 38, in __init__
SerialBase.__init__(self, *args, **kwargs)
File "C:\Python33\lib\site-packages\serial\serialutil.py", line 282, in __init__
self.open()
File "C:\Python33\lib\site-packages\serial\serialwin32.py", line 66, in open
raise SerialException("could not open port %r: %r" % (self.portstr, ctypes.WinError()))
serial.serialutil.SerialException: could not open port 'COM3': FileNotFoundError(2,   'The system cannot find the file specified.', None, 2)

This is probably something easy to fix and I have looked pretty much everywhere and I still can't seem to find the answer to the problem.

Adding what your device manager shows might help more

Nipun Batra
– Nipun Batra

2014-01-01 15:34:14 +00:00
Commented Jan 1, 2014 at 15:34 — Nipun Batra
– Nipun Batra, Commented Jan 1, 2014 at 15:34

Daniel Roseman · Accepted Answer · 2014-01-01 14:44:53Z

1

Why are you trying to use "COM3" on a Linux machine? That's a Windows port name. Linux/Unix port names are of the form /dev/ttyUSB0.

But, as the docs show, you can probably just use the port number directly - they start at 0, so you can do ser = serial.Serial(2, 9600).

answered Jan 1, 2014 at 14:44

Daniel Roseman

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1 Comment

user2387537 Over a year ago

I'm not using a Linux machine, I'm using Windows 8 and when I put ser = serial.Serial(2, 9600) I get Access is denied. @DanielRoseman

daemor · Accepted Answer · 2014-01-03 13:21:07Z

0

If you have the arduino ide open, then python may not be able to access the port. Ive hade this problem as well using Processing.

answered Jan 3, 2014 at 13:21

daemor

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