Converting data from serial/usb using PySerial

Question

I have a UBlox receiver connected to my computer and I am trying to read it using PySerial however I am new to python and was hoping to get some clarification/help on understanding the data.

My code looks like:

import serial
# open the connection port
connection = serial.Serial('/dev/ttyACM0', 9600)
# open a file to print the data. I am doing this to make
# sure it is working
file1 = open('output_file', 'wb+')
# All messages from ublox receivers end with a carriage return
# and a newline 
msg = connection.readline()
# print the message to the file
print >> file1, msg

What I get in the file, and when I print the 'type' of msg it is a list:

['\\xb5b\\x01\\x064\\x00\\xe0\\x88\\x96#\\xd3\\xb9\\xff\\xffX\\x07\\x03\\xdd6\\xc31\\xf6\\xfd)\\x18\\xea\\xe6\\x8fd\\x1d\\x00\\x01\\x00\\x00\\x00\\x00\\x00\\x00\\xfd\\xff\\xff\\xff\\x01\\x00\\x00\\x00\\x02\\x00\\x00\\x00p\\x00\\x02\\x0f\\x16\\xa2\\x02\\x00\\x9c\\xeb\\xb5b\\x01\\x07\\\\x00\\xe0\\x88\\x96#\\xe0\\x07\\x01\\x17\\x15237\\x04\\x00\\x00\\x00\\xd6\\xb9\\xff\\xff\\x03\\x01\\n']

["\\x1a\\x0c\\x04\\x19'y\\x00$\\xf7\\xff\\xff\\x1a\\x1d\\x04\\x01\\x00\\x007\\x00\\x00\\x00\\x00\\x00\\x02\\x1f\\x0c\\x01\\x00+:\\x00\\x00\\x00\\x00\\x00\\x01 \\r\\x07&-\\x9f\\x00\\xff\\x01\\x00\\x00\\x17\\xc1\\x0c\\x04\\x16\\n"]

In order to interpret/decode the ublox messages have two format types. Some of the messages are in NMEA format(basically comma delimited)

$MSG, 1, 2, 3, 4

Where the other messages are straight hexidecimal, where each byte or set of bytes represent some information

[AA BB CC DD EE]

So my question is: is there a way I can interpret/convert the data from serial connection to a readable or more usable format so I can actually work with the messages. Like I said, I am new to python and more used to C++ style strings or array of characters

`

Answer 1

A typical parsing task. In this case, it'll probably be the simplest to make tokenization two-stage:

1. read the data until you run into a message boundary (you didn't give enough info on how to recognize it)
2. split the read message into its meaningful parts
   • for type 1, it's likely re.split(", *",text)
   • for type 2, none needed
3. display the parts however you want

---

Regarding why serial.Serial.readline returns a list. I consulted the sources - serial.Serial delegates readline to io.IOBase , and its source indeed shows that it should return a bytestring .

So, the function might be overridden in your code by something. Eg what do print connection.readline and print serial.Serial.readline show?