Only write when serial device outputs data

Question

I am trying to make a data-logger than writes the output from a serial device that only outputs once per minute. I need it to have a time stamp on the output. The code I have so far will log the output but it keeps logging blanks with a timestamp in-between the device's output. How do I get it to only write a line with the timestamp when the device has output?

#!/usr/bin/env python
Log data from serial port

import argparse
import serial
import datetime
import time
import os
timestr = time.strftime("%Y%m%d")
Tstamp = time.strftime("%Y/%m/%d %H:%M ")

parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument("-d", "--device", help="device to read from", default="/dev/ttyUSB0")
parser.add_argument("-s", "--speed", help="speed in bps", default=9600, type=int)
args = parser.parse_args()

outputFilePath = os.path.join(os.path.dirname(__file__),
                 datetime.datetime.now().strftime("%Y-%m-%d") + ".csv")

with serial.Serial(args.device, args.speed) as ser, open(outputFilePath,'w') as outputFile:
    print("Logging started. Ctrl-C to stop.") 
    try:
        while True:
            time.sleep(1)  
            x = (ser.read(ser.inWaiting()))
            data = x.decode('UTF-8')          
            outputFile.write(Tstamp + " "  + data + '\n')
            outputFile.flush()
    except KeyboardInterrupt:
        print("Logging stopped")

Sorry for the poor formatting I am not sure how to make it look right on here.

Answer 1

By adding if x!= "" and indenting properly I got it to work. Now I just need ot fix it to append the file and not overwrite it.

#!/usr/bin/env python
# Log data from serial port


import argparse
import serial
import datetime
import time
import os


parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument("-d", "--device", help="device to read from", default="/dev/ttyUSB0")
parser.add_argument("-s", "--speed", help="speed in bps", default=9600, type=int)
args = parser.parse_args()

outputFilePath = os.path.join(os.path.dirname(__file__),
                 datetime.datetime.now().strftime("%Y-%m-%d") + ".csv")

with serial.Serial(args.device, args.speed) as ser, open(outputFilePath,'w') as outputFile:
    print("Logging started. Ctrl-C to stop.") 
    try:
        while True:
            time.sleep(1) 
            x = (ser.read(ser.inWaiting())) 
            data = x.decode('UTF-8')
            if data !="":
                outputFile.write(time.strftime("%Y/%m/%d %H:%M ") + " " + data  )
                outputFile.flush()

    except KeyboardInterrupt:
        print("Logging stopped")