By Nyxynyx

2014-06-13 22:34:07 8 Comments

Currently the python program must know which port a device (Arduino) is on before Python can communicate the device.

Problem: Whenever the device is plugged out and back in, its COM port changes, so the correct serial port must be given to Python again for it to find the device.

How can Python (using pySerial) automatically search for the correct serial port to use? Is it possible for python to correctly identify the device on a serial port as an Arduino?


@Matt Williams 2014-08-04 05:06:44

Use the following code to see all the available serial ports:

ports = list(
for p in ports:
    print p

This gives me the following:

('COM4', 'Arduino Due Programming Port (COM4)', 'USB VID:PID=2341:003D SNR=75330303035351300230')
('COM11', 'RS-232 Port (COM11)', 'FTDIBUS\\VID_0856+PID_AC27+BBOPYNPPA\\0000')

To work out if it's an Arduino you could do something like:

    if "Arduino" in p.description:
        print "This is an Arduino!"

@Matt Williams 2014-08-04 05:11:20

This also works if you're plugged into the Native USB port on the Arduino Due. I haven't tested it on any other Arduino's.

@Eric 2016-12-03 23:22:49

p[1] is better spelt p.description

@Daniel B. 2020-04-26 04:35:00

If you check p.hwid for "VID:PID=2341:0043", that is an arduino uno, and that will work with the knockoffs as well. You would need to use a different PID (just scan your ports like in the post to find the correct one).

@Eric 2016-11-10 15:18:30

Using, we can find and connect to an arduino with:

import warnings
import serial

arduino_ports = [
    for p in
    if 'Arduino' in p.description  # may need tweaking to match new arduinos
if not arduino_ports:
    raise IOError("No Arduino found")
if len(arduino_ports) > 1:
    warnings.warn('Multiple Arduinos found - using the first')

ser = serial.Serial(arduino_ports[0])

If you know you're looking for exactly the same arduino each time, you can filter on p.serial_number instead


def find_arduino(serial_number):
    for pinfo in
        if pinfo.serial_number == serial_number:
            return serial.Serial(pinfo.device)
    raise IOError("Could not find an arduino - is it plugged in?")

ser = find_arduino(serial_number='85430353531351B09121')

@dust 2016-12-06 19:08:50

Works very nice, but only for original Arduino. Non-original Arduinos will report differently, e.g. "Generic CDC"... ultimately the best solution would be to list all possible USB devices and then allow a user to pick one using a runtime flag.

@Eric 2016-12-07 13:39:26

@dust: Right, but for the common case where you're bouncing one piece of hardware between multiple USB ports and computers, this technique is most convenient. If you're looking to detect previously-unseen arduino-like devices, you're going to have a harder time, and forcing the user to choose as you mention is probably the best path

@Espen 2019-04-16 13:36:28

Is it possible to program the description given from the Arduino? Then each python will find and connect to the exact Arduino it needs.

@Pardeep Singh 2019-02-14 08:02:30

Try this code (only for windows users. MAC user can withdraw idea from this concept)

import serial
import time

ser = serial.Serial()

ser.baudrate = 9600


while True:
    ser.port = list[i]
        if ser.isOpen()==True:
            #print('arduino is on COMPORT'.join(i))

        if i==18:
            print('Kindly remove usb cable and try again')

print('here we go')
while True:

@Joseph F. Mack 2016-01-29 17:46:12

Written on a Windows 10 Computer, Python 2.7.9 Version.

This program automatically detects and lists ports.  If no ports are found, it simply shells out.  In the printout below "list(" finds two ports and the program lists them out - a listout shown below:

     COM5 - USB-SERIAL CH340 (COM5)
     Found Arduino Uno on COM5
     COM4 - Microsoft USB GPS Port (COM4)

As each port is found, "CH340," (the name of the Adruino Uno) is searched for in the listed port with the "while int1 < 9:" loop.  The first "If" statement looks for "CH340" and when found the integer value "int1" will be the same as the com port #. With a concatination,  the operation "str1 = "COM" + str2" gives the com port name of the Adruino, eg. "COM5."  The next "IF" statement looks for both "CH340" AND str1, ("COM5") in the above case.  The statement "Found Arduino Uno on COM5" prints out, and "str1" is used in setting up the com port:

ser = serial.Serial(str1, 9600, timeout=10)

This program goes on to open the com port and prints data from the Adruino.

The modules "serial, sys, time," must all be imported.

Written by Joseph F. Mack 01/29/2016.  "A BIG Thank you" to all the individuals whose programs I "borrowed" from that are available in the many forums for Python and PYGame users!

import serial
import sys
import time

serPort = ""
int1 = 0
str1 = ""
str2 = ""

# Find Live Ports
ports = list(
for p in ports:
   print p # This causes each port's information to be printed out.
           # To search this p data, use p[1].

   while int1 < 9:   # Loop checks "COM0" to "COM8" for Adruino Port Info. 

      if "CH340" in p[1]:  # Looks for "CH340" in P[1].
            str2 = str(int1) # Converts an Integer to a String, allowing:
            str1 = "COM" + str2 # add the strings together.

      if "CH340" in p[1] and str1 in p[1]: # Looks for "CH340" and "COM#"
         print "Found Arduino Uno on " + str1
         int1 = 9 # Causes loop to end.

      if int1 == 8:
         print "UNO not found!"
         sys.exit() # Terminates Script.

      int1 = int1 + 1

time.sleep(5)  # Gives user 5 seconds to view Port information -- can be   changed/removed.

# Set Port
ser = serial.Serial(str1, 9600, timeout=10) # Put in your speed and timeout value.

# This begins the opening and printout of data from the Adruino.

ser.close()  # In case the port is already open this closes it.   # Reopen the port.


int1 = 0
str1 = ""
str2 = ""

while int1==0:

   if "\n" not in str1:        # concatinates string on one line till a line feed "\n"
      str2 = ser.readline()    # is found, then prints the line.
      str1 += str2

print 'serial closed'

@acpilot 2016-04-19 19:19:36

I assume this program is run on the computer plugged into the Arduino. Is that right? What extension is used to save this file?

@Eric 2016-11-10 15:14:28

This is terribly-written code. int<n> is not a sensible variable name, and 8 and 9 are deeply magic numbers

@AlwaysLearning 2018-12-22 12:36:23

This code won't work for genuine Arduinos. Genuine Arduinos use FTDI USB-Serial bridges whereas the CH340/CH341 serial ports are Jiangsu Qinheng chips and are found only on cheap Chinese Arduino "clones."

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