I have some code (shown below) which turns the Raspberry Pi into a datalogger. I use GPIO.add_event_detect to detect the date and time that a square wave signal changes state. This data is then saved to a CSV file continuously as each state change is detected. However if I turn the Raspberry Pi off or stop the program from running, when I then turn it back on again the previous CSV file is overwritten by a new file. Does anyone know how I could create a new CSV file every time I reboot the program/Pi?

import RPi.GPIO as GPIO
import datetime
from datetime import timedelta
import time
from time import sleep
import csv
from csv import writer

# endTime = datetime.datetime.now() + datetime.timedelta(seconds=60)

def my_callback(channel):
     data_writer([GPIO.input(40), datetime.datetime.now()])      # writes the detected
     # edge event to a CSV file with columns of rise/fall and the date & time of detection

if __name__ == '__main__':

    GPIO.setmode(GPIO.BOARD)       # set up GPIO numbering (BOARD = physical pins on Pi)
    GPIO.setup(40, GPIO.IN)         # set physical pin 40 as input

# create CSV file to write edge detection data to called Datalogger, with data on new line
    with open('/media/pi/KINGSTON/datalogger.csv', 'w', newline='') as Datalogger:
        data_writer = writer(Datalogger)

        data_writer.writerow(["Edge type", "Date & Time"])       # create headers in CSV file

        GPIO.add_event_detect(40, GPIO.BOTH, callback=my_callback)     # edge detection function
        # detects both rise and fall in signal on pin 40, then runs my callback

        while True:
# main program loop here - loops detection of edges then runs my callback
          # if datetime.datetime.now() >= endTime:
              # break
              # exit()

1 Answer 1


You need to open the file in append mode, not overwrite mode.

Change the mode in the open statement from w to a:

open('/media/pi/KINGSTON/datalogger.csv', 'a',  newline='')
  • Thanks for your response. Would this just keep appending the very first CSV file I make? When I run my script it creates a CSV file and continuously populates it with data. However when I stop the script and then restart it, it overwrites the previous CSV file. I would like to keep the original CSV file but then create a new CSV file on every reboot.
    – user93154
    Commented Nov 1, 2018 at 10:16
  • If you want a new file, then you should state that in the question. If you want a new file bot keep the old file, then the solution is to use a different file name.
    – RalfFriedl
    Commented Nov 1, 2018 at 10:18
  • Simplest way is to add the date and time to the filename.
    – CoderMike
    Commented Nov 1, 2018 at 10:22
  • Hi @Dan, if the answer help you, then you should accept it.
    – Ingo
    Commented Nov 1, 2018 at 11:42

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