Python - error handling

Question

I am trying to use a python script on a Pi and Windows to pull csv data hosted on an internal site however after a while of pulling the data ( on both linux and windows ) there seems to be a glitch where it doesn't process ( which im trying to figure out or have a work around for ) and my script fails with IndexError: list index out of range which i'm assuming is because my script can't access the HTTP site - however if i run the application as soon as it fails it's fine and will run again and fail after a random amount of time usually ~ 2h

Here is a snip of the code i'm using: - All i want from the CSV is the last line of data

import csv
import time
import math
import subprocess
import datetime
import requests
from contextlib import closing


def exec_code():



     url = "http://xx.xx.xx.xx/daily.csv"
     l = []
     with closing(requests.get(url, stream=True)) as r: 
         reader = csv.reader(r.iter_lines(), delimiter=',', quotechar='"')
         for index,line in enumerate(reader): #This iterates the file line by line which is memory efficient in case the csv is huge.
             if index < 0: #removes header if 1 adds header
                 l.append(line)
         if index > 1: # means the file has at least 3 lines
             l.append(line)


     #creates variables
         for row in l:
          Time = row[0]
          Temp = row[5]



if __name__ == '__main__':
    while True:
        exec_code()
        time.sleep(60)

Is there a way instead of the application crashing when there is no indexes to sleep for 5 seconds and then try again?

thank you

You don't show the full error traceback, so we can't be certain which line it is from, but my guess is these lines Time = row[0] Temp = row[5] are probably the issue. Check the number of elements before indexing. — cdarke
– cdarke, Commented Jan 29, 2018 at 23:47

John R · Accepted Answer · 2018-01-29 23:52:37Z

1

To answer your question, Python error handling is best addressed with the try, except syntax.

try:
    whatever you are trying to do
except:
    do this on error

It sounds like you might need to use a while flag in conjunction with this, however, if you want Python to continue trying until success:

flag = False
while not flag:
    try:
        whatever you are trying to do
        flag = True
    except:
        do this on error
        time.sleep(5)

answered Jan 29, 2018 at 23:52

John R

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