Create a List that contain each Line of a File

Question

I'm trying to open a file and create a list with each line read from the file.

   i=0
   List=[""]
   for Line in inFile:
      List[i]=Line.split(",")
      i+=1
   print List

But this sample code gives me an error because of the i+=1 saying that index is out of range. What's my problem here? How can I write the code in order to increment my list with every new Line in the InFile?

score 92 · Accepted Answer · edited Apr 23 '11 at 00:04

92

It's a lot easier than that:

List = open("filename.txt").readlines()

This returns a list of each line in the file.

edited Apr 23 '11 at 00:04

David Hall

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answered Nov 29 '08 at 22:03

Brian C. Lane

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WoooW Just perfect! It worked. Btw imagine that was not a file... But i wnat to creat a dynamic list... How can I append an element on it? like if was an arrayList? ty so much – UcanDoIt Nov 29 '08 at 22:06
The append method will do the trick. For example: xs.append(line) – Eli Courtwright Nov 29 '08 at 23:06
4

what about closing the file ? – matlabit Nov 25 '15 at 13:44
5

No need to close it, python handles that automatically when the file goes out of scope. – Brian C. Lane Dec 04 '15 at 17:39
5

Is there any way to strip the "/n" from the list generated ? – Udit Hari Vashisht Oct 03 '18 at 18:45
this is legacy code, right? it wont let me do this as `with open` – oldboy May 23 '21 at 23:35

score 65 · Answer 2 · answered Aug 10 '15 at 15:22

65

I did it this way

lines_list = open('file.txt').read().splitlines()

Every line comes with its end of line characters (\n\r); this way the characters are removed.

answered Aug 10 '15 at 15:22

Absulit

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4

Thanks, this removes the newlines as I had expected from the accepted answer :) +1 for you – Stan Smulders Nov 06 '18 at 12:52

score 11 · Answer 3 · answered Nov 29 '08 at 22:06

11

my_list = [line.split(',') for line in open("filename.txt")]

answered Nov 29 '08 at 22:06

orip

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I fear jumping into a list comprehension for someone still trying to understand basic python might be a bit large of a step. :) – Dustin Nov 29 '08 at 22:08
Dustin is right, however orip offered the most correct answer to the question. – tzot Nov 30 '08 at 08:23
I really like this method. However, at the end of each list, a `\n` is printed next to the last value on the line. How can I remove it? – interstellar Mar 27 '16 at 15:52

score 10 · Answer 4 · answered Nov 29 '08 at 22:07

Please read PEP8. You're swaying pretty far from python conventions.

If you want a list of lists of each line split by comma, I'd do this:

l = []
for line in in_file:
    l.append(line.split(','))

You'll get a newline on each record. If you don't want that:

l = []
for line in in_file:
    l.append(line.rstrip().split(','))

score 1 · Answer 5 · answered Nov 29 '08 at 22:06

1

A file is almost a list of lines. You can trivially use it in a for loop.

myFile= open( "SomeFile.txt", "r" )
for x in myFile:
    print x
myFile.close()

Or, if you want an actual list of lines, simply create a list from the file.

myFile= open( "SomeFile.txt", "r" )
myLines = list( myFile )
myFile.close()
print len(myLines), myLines

You can't do someList[i] to put a new item at the end of a list. You must do someList.append(i).

Also, never start a simple variable name with an uppercase letter. List confuses folks who know Python.

Also, never use a built-in name as a variable. list is an existing data type, and using it as a variable confuses folks who know Python.

answered Nov 29 '08 at 22:06

S.Lott

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How can I leanr about python coding standards? Thanks, i didn't know you use varaibable names in lowercase... any special reason for that? Ty – UcanDoIt Nov 29 '08 at 22:09
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While you're on conventions, PEP8 also has something to say about spaces inside of parentheses. :) – Dustin Nov 29 '08 at 22:11
See http://www.python.org/dev/peps/pep-0008/, also see http://stackoverflow.com/questions/159720/what-is-the-naming-convention-in-python-for-variable-and-function-names – S.Lott Nov 29 '08 at 22:12
@Dustin: well aware of space-in-parenthesis recommendation in PEP8. After 3 decades of spaces in ()'s, I'm not going to change. – S.Lott Nov 29 '08 at 22:13
@Federico People who read your code and stop to think about why some parts look different from the rest of the code. :) e.g. what's special about the len() call that makes it consistent with PEP8, but inconsistent with the lines above it? If you don't care, just follow the conventions. :) – Dustin Nov 29 '08 at 23:03
@Dustin: Yes, trivial spacing inconsistencies are inconsistent. I've seen so much code that simply doesn't work in the first place. I feel that "working" trumps "consistent spacing". If spacing leads to difficulty understanding, then there are larger problems to solve first. – S.Lott Nov 30 '08 at 03:41

score 1 · Answer 6 · answered Nov 29 '08 at 22:07

1

f.readlines() returns a list that contains each line as an item in the list

if you want eachline to be split(",") you can use list comprehensions

[ list.split(",") for line in file ]

answered Nov 29 '08 at 22:07

hasen

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score 1 · Answer 7 · answered Aug 07 '17 at 12:36

1

Assuming you also want to strip whitespace at beginning and end of each line, you can map the string strip function to the list returned by readlines:

map(str.strip, open('filename').readlines())

answered Aug 07 '17 at 12:36

Jonathan Koren

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Din · Answer 8 · 2008-11-29T22:16:09.717

-9

I am not sure about Python but most languages have push/append function for arrays.

edited Nov 29 '08 at 22:16

answered Nov 29 '08 at 22:01

Din

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Create a List that contain each Line of a File

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