Why I get a list index error, if the code runs fine?

Question

I have 7 txt data files, and I want to compute the standard deviation of the numbers in the second column, for each file.

I wrote this code:

from pathlib import Path
destdir = Path()
files = [p for p in destdir.iterdir() if p.is_file()]
for p in files:
    with p.open() as f:
        adatok=[]
        for i in f:
            adatok.append(float(i.split()[1]))
            
        atlag=sum(adatok)/len(adatok)
        
        elofordulas=[]
        for j in adatok:
            if j not in elofordulas:
                elofordulas.append(j)
                
        asd1=[]
        
        for j in elofordulas:
            asd1.append(adatok.count(j)*((atlag-j)**2))
            
        szoras=sqrt(sum(asd1)/len(adatok))
        
        print(p)
        
        print(szoras)
        
        print('-------')

It runs fine, but I get this error:

IndexError
Traceback (most recent call last)
in ()
6 adatok=[]
7 for i in f:
—-> 8 adatok.append(float(i.split()1))
9
10 atlag=sum(adatok)/len(adatok)

IndexError: list index out of range

Why? And what should I do?

Edit: This is a part of my data file, all lines are the same

Asked By: Medve

||

Source

Answer 1

I bet you got a line without a space or a tab in one of your csv files. To be sure, just do some exception handling:

import sys
from math import sqrt
from pathlib import Path

if __name__ == '__main__':

    destdir = Path()
    files = [p for p in destdir.iterdir() if p.is_file()]

    for p in files:
        with p.open() as f:
            adatok = []
            for line_no, line in enumerate(f, start=1):
                try:
                    adatok.append(float(line.split()[1]))
                except Exception as e:
                    print(f"Exception '{e}' in line {line_no} of file '{p}' reading '{line.strip()}'")
                    sys.exit(-1)

        atlag = sum(adatok) / len(adatok)

        elofordulas = []
        for j in adatok:
            if j not in elofordulas:
                elofordulas.append(j)

        asd1 = []

        for j in elofordulas:
            asd1.append(adatok.count(j) * ((atlag - j) ** 2))

        szoras = sqrt(sum(asd1) / len(adatok))

        print(p)
        print(szoras)
        print('-------')

Update: We found that the stack trace was a bit misleading. The real mistake was that files contained all files in the current folder. This, of course, included the Python script itself.

Lesson learned: When parsing multiple data file, proper exception handling is important.

With the proposed exception handling, the error would have been something like
Exception 'list index out of range' in line 1 of file 'script.python' reading 'import' making it more obvious, where to look for the mistake.

Answered By: Lydia van Dyke

Why I get a list index error, if the code runs fine?

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