serial_split.py

from __future__ import print_function
import serial

# This script is intended to redirect a specially demarcated section
# of the serial stream to STDERR, which you can then redirect to
# wherever you wish (like a text file for importing into Excel).

# host usage:
# python serial_split.py 2> mydata.txt

# client serial stream example:
#
# Program starting...
# blah blah blah
# Data next!
# ++++++++++++++++++++
# num, something, column
# 1,2,3
# 1,4,9
# 1,8,27
# ====================
# Program done, shutting down
# Thanks!

start_sequence = '++++++++++++++++++++'
end_sequence =   '===================='
device = serial.Serial('/dev/ttyUSB0', 115200)

logging = False

while True:
    line = device.readline()
    print(line)
    
    if logging == False and line == start_sequence:
        logging = True
        continue  # make sure that we do not log the start sequnce
    elif logging == True and line == stop_sequence:
        logging = False
        
    if logging:
        print(line, file=sys.stderr)