Read data from serial port using Python

Hello everyone!

I would like to intercept data going to a serial printer using Python and read it...

If this is possible which kind of tools / resources you suggest me to use / learn?
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Please answer / clarify each question so that it will be easier to help:

1.) you have a serial printer connected to a PC?
2.) What is your operating system?
3.) You have an application, that can print to your printer?
4.) printing is successful with that application?
5.) you want to print from that application and monitor what is going on the serial port, while the printer is connected and printing?
ltpittAuthor Commented:
1) Yes, the serial printer is connected to a pc
2) The pc connected to the printer is linux, the other pc I'd want to use will be probably a Raspberry Pi with Linux too
3 & 4) The pc connected to the printer can print without problems
5) No: I simply want to connect the Raspberry Pi instead of the printer and get the data instead of the printer
I don't know a lot about serial printers.
The main question is whether the printer sends data back to the PC or not.

If the printer is a passive device and does not send any data, then things should be simple.
There's a module called pyserial  ( , which should do the job.

Do you know the configuration of the serial printer?
number of data bits
number of stop bits
configuration of parity bit

I would suggest to install python virtualenv on your raspberry pi.
It's better for testing / debugging / keeping your python setup clean.

# install virtualenv
sudo apt-get install python-virtualenv

# install python dev.  and build-essential This is normally required if you want to install python packages with C-code.
sudo apt-get install python-dev build-essential

# create a virtualenv
virtualenv ~/mypython

# activate your virtualenv. You have to do this everytime you want use this particular  virtualenv
source ~/mypython/bin/activate

# install pyserial
pip install pyserial   # if this fails, then please send the error messages.
                                    # perhaps some build dependencies are missing.

a simple script to read data and write it to the screen should look like:

#/usr/bin/env python
import serial

ser = serial.Serial('/dev/ttyS1', 19200, timeout=1)
while True:
    char =
    if char:

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ltpittAuthor Commented:
It looks clear and straightforward!

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