Python 2.7 String Index Error

Question

I'm writing a program to choose a random line from a text file using a while loop as a counter and then another variable to choose the random line:

import random 


fortunes_file = open("fortunes.txt", "r")


fortunes = fortunes_file.readline()

count = 0


while fortunes != "":
    count += 1
    fortunes = fortunes_file.readline()

rand_line = random.randint(1, count)

print fortunes[rand_line]

fortunes_file.close()

However, I get the following error when trying to run the program:

IndexError: string index out of range

Burhan Khalid · Accepted Answer · 2016-01-10 09:25:58Z

2

You need readlines() not readline(); but actually you can highly simplify your code:

import random

with open('fortunes.txt') as f:
   fortunes = list(f)

print(random.choice(fortunes))

Or, if you prefer the readlines() version:

import random

f = open('fortunes.txt')
fortunes = f.readlines()
f.close()

print(random.choice(fortunes))

answered Jan 10, 2016 at 9:25

Burhan Khalid

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Comments

Eugene Yarmash · Accepted Answer · 2016-01-10 09:46:46Z

1

You're overwriting fortunes on each iteration of the while loop. At the EOF .readline() returns an empty string, therefore fortunes[rand_line] raises the IndexError. You could use .readlines() instead (or just use the file object as an iterator):

with open("fortunes.txt", "r") as fortunes_file:
    fortunes = fortunes_file.readlines()  # alternatively, use list(fortunes_file)
print(random.choice(fortunes))

edited Jan 10, 2016 at 9:46

answered Jan 10, 2016 at 9:23

Eugene Yarmash

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Comments

Remi Guan · Accepted Answer · 2016-01-10 09:32:11Z

The problem is here:

fortunes = fortunes_file.readline()

...

    fortunes = fortunes_file.readline()

You just re-defined the variable, so after that while loop end, fortunes actually is the last line in your file.

You can simply use io.IOBase.readlines() to read the file into a list line-by-line, and use random.choice() to choose an element in a list randomly. You don't need a counter and slice the list yourself.

For example:

import random   

# use `with` is recommended here since you don't need close the file manually
with open("fortunes.txt", "r") as f:
    fortunes = fortunes_file.readlinse()

print random.choice(fortunes)

However, if you also want to know how to fix your code, just put the output of io.IOBase.readline() into a list like below:

import random 


fortunes_file = open("fortunes.txt", "r")    

fortunes = []
fortunes.append(fortunes_file.readline())   
count = 0


while fortunes != "":
    count += 1
    fortunes.append(fortunes_file.readline())

rand_line = random.randint(1, count)

print fortunes[rand_line]   
fortunes_file.close()

Note that if you don't want use .readlines() and random.choice(), you still don't need that counter, you can also use len(fortunes) to get the length of your list instead of write a useless counter yourself.

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