Value Error : invalid literal for int() with base 10: ''

Question

I'm new in Python and I don't know why I'm getting this error sometimes.

This is the code:

import random
sorteio = []
urna = open("urna.txt")

y = 1
while y <= 50:
    sort = int(random.random() * 392)
    print sort
    while sort > 0:
        x = urna.readline()
        sort = sort - 1
    print x  
    sorteio = sorteio + [int(x)]
    y = y + 1
print sorteio

Where urna.txt is a file on this format:

I'll be grateful if anyone knows why this error appears and how to fix it.

is your goal to read in the text file and sort only a random part of the values? are you aware that you are only storing the last value that you read out? — Ryan Haining, Jul 17 '13 at 16:33
yes, but i tought that "sorteio = sorteio + [int(x)]" was storing all values in a list... how can i store then all? — Matheus Corrêa, Jul 17 '13 at 17:59
Could you tell me what the point of the `while <= 50` is here? Could you post your expected output, that would help in solving your problems — Ryan Haining, Jul 17 '13 at 18:05
I have to randomly select 50 numbers urna.txt file (each one represents an id in a db) and stores them in a list and then retrieve the data for each id and print them — Matheus Corrêa, Jul 17 '13 at 18:20
i guess i've just figure out another problem: the random search has to be all over the file every time, but the way i coded the next loop will be on a smaller part of the file, right? — Matheus Corrêa, Jul 17 '13 at 18:25
are you saying start on the `sort`th line and read the next 50 values after it? — Ryan Haining, Jul 17 '13 at 18:39

Ryan Haining · Answer 1 · 2013-07-17T20:55:32.947

2

Upon attempting to read past the end of the file, you're getting an empty string '' which cannot be converted to an int.

>>> int('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: ''

to satisfy the requirement of selecting 50 random lines from the text value, if I understand your problem correctly:

import random

with open("urna.txt") as urna:
    sorteio = [int(line) for line in urna] # all lines of the file as ints

selection = random.sample(sorteio, 50)

print selection

edited Jul 17 '13 at 20:55

answered Jul 17 '13 at 18:37

Ryan Haining

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2

`random.sample` would be a more direct way to get a specific number of randomly chosen items. – Blckknght Jul 17 '13 at 19:59
1

In general, it is much easier to use a `for` loop to loop over the lines of a file. Ryan's answer uses a list comprehension which contains a `for` loop, but you can also write it as `for line in file:` just like you would for other `for` loops. Just for reference. – 2rs2ts Jul 17 '13 at 21:02

score 1 · Answer 2 · edited May 23 '17 at 11:49

1

.readline() returns an empty string when you come to the end of the file, and that is not a valid number.

Test for it:

if x.strip():  # not empty apart from whitespace
    sorteio = sorteio + [int(x)]

You appear to beappending to a list; lists have a method for that:

sorteio.append(int(x))

If you want to get a random sample from your file, there are better methods. One is to read all values, then use random.sample(), or you can pick values as you read the file line by line all the while adjusting the likelihood the next line is part of the sample. See a previous answer of mine for a more in-depth discussion on that subject.

edited May 23 '17 at 11:49

Community

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answered Jul 17 '13 at 16:00

Martijn Pieters

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i added this line on the code and it runs, but the results are not what i was expecting... the result i'm looking for is something like this: to read in the text file and sort only a random part of the values and add then to a list. the result i got is only the strings that are "pure numbers" (whithout whitespaces or "\n" for example) – Matheus Corrêa Jul 17 '13 at 18:07

Value Error : invalid literal for int() with base 10: ''

2 Answers2