pyserial - How to read the last line sent from a serial device

Perhaps I'm misunderstanding your question, but as it's a serial line, you'll have to read everything sent from the Arduino sequentially - it'll be buffered up in the Arduino until you read it.

If you want to have a status display which shows the latest thing sent - use a thread which incorporates the code in your question (minus the sleep), and keep the last complete line read as the latest line from the Arduino.

Update: mtasic's example code is quite good, but if the Arduino has sent a partial line when inWaiting() is called, you'll get a truncated line. Instead, what you want to do is to put the last complete line into last_received, and keep the partial line in buffer so that it can be appended to the next time round the loop. Something like this:

def receiving(ser):    global last_received    buffer_string = ''    while True:        buffer_string = buffer_string + ser.read(ser.inWaiting())        if '\n' in buffer_string:            lines = buffer_string.split('\n') # Guaranteed to have at least 2 entries            last_received = lines[-2]            #If the Arduino sends lots of empty lines, you'll lose the            #last filled line, so you could make the above statement conditional            #like so: if lines[-2]: last_received = lines[-2]            buffer_string = lines[-1]

Regarding use of readline(): Here's what the Pyserial documentation has to say (slightly edited for clarity and with a mention to readlines()):

Be careful when using "readline". Do specify a timeout when opening the serial port, otherwise it could block forever if no newline character is received. Also note that "readlines()" only works with a timeout. It depends on having a timeout and interprets that as EOF (end of file).

which seems quite reasonable to me!

from serial import *from threading import Threadlast_received = ''def receiving(ser):    global last_received    buffer = ''    while True:        # last_received = ser.readline()        buffer += ser.read(ser.inWaiting())        if '\n' in buffer:            last_received, buffer = buffer.split('\n')[-2:]if __name__ ==  '__main__':    ser = Serial(        port=None,        baudrate=9600,        bytesize=EIGHTBITS,        parity=PARITY_NONE,        stopbits=STOPBITS_ONE,        timeout=0.1,        xonxoff=0,        rtscts=0,        interCharTimeout=None    )    Thread(target=receiving, args=(ser,)).start()

You can use ser.flushInput() to flush out all serial data that is currently in the buffer.

After clearing out the old data, you can user ser.readline() to get the most recent data from the serial device.

I think its a bit simpler than the other proposed solutions on here. Worked for me, hope it's suitable for you.