sorting lines of file python

Question

I want to Bubblesort a file by numbers and I have propably 2 mistakes in my code.

The lines of the file contain: string-space-number

The response is a wrong sorting or sometimes I got also an IndexError because x.append(row[l]) is out of range

Hope someone can help me

Code:

#!/usr/bin/python
filename = "Numberfile.txt"
fo = open(filename, "r")

x, y, z, b = [], [], [], []

for line in fo:             # read
   row = line.split(" ")    # split items by space
   x.append(row[1])         # number


liste = fo.readlines()
lines = len(liste)
fo.close()

for passesLeft in range(lines-1, 0, -1):
    for i in range(passesLeft):
        if x[i] > x[i+1]:
                temp = liste[i]
                liste[i] = liste[i+1]
                liste[i+1] = temp

fo = open(filename, "w")
for i in liste:
    fo.writelines("%s" % i)
fo.close()

Nir Alfasi · Accepted Answer · 2015-07-15 16:00:14Z

1

Seems that you have empty lines in the file.

Change:

for line in fo:             # read
   row = line.split(" ")    # split items by space
   x.append(row[1])         # number

with:

for line in fo:             # read
   if line.strip():
       row = line.split(" ")    # split items by space
       x.append(row[1])         # number

By the way, you're better off using re.split with the regex \s+:

re.split(r'\s+', line)

which will make your code more resilient - it will be able to handle multiple spaces as well.

For the second issue Anand proceeded me: you're comparing strings, if you want to compare numbers you'll have to wrap it with a call to int()

edited Jul 15, 2015 at 16:00

answered Jul 15, 2015 at 15:45

Nir Alfasi

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Nir Alfasi Over a year ago

@SadCroco after you run into it many times (and hammer your head against the wall like I did each time...) - you'll finally get it ;)

Anand S Kumar · Accepted Answer · 2015-07-15 15:51:26Z

1

First issue, if you are sorting based on the numbers and the numbers can be multiple digits, then your logic would not work because x is a list of strings , not integers, and when comparing strings, it compares lexicographically, that is '12' is less than 2 , etc. You should convert the number to int before appending to x list.

Also if you are getting ListIndex error, you may have empty lines or lines without 2 elements, you should correctly check you input, also you can add a condition to ignore the empty lines.

Code -

for line in fo:
   if line.strip():
       row = line.split(" ")
       x.append(int(row[1]))

answered Jul 15, 2015 at 15:51

Anand S Kumar

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