End-line characters from lines read from text file, using Python

Question

When reading lines from a text file using python, the end-line character often needs to be truncated before processing the text, as in the following example:

f = open("myFile.txt", "r")
for line in f:
    line = line[:-1]
    # do something with line

Is there an elegant way or idiom for retrieving text lines without the end-line character?

Asked By: pythonquick

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Source

Answer 1

What’s wrong with your code? I find it to be quite elegant and simple. The only problem is that if the file doesn’t end in a newline, the last line returned won’t have a 'n' as the last character, and therefore doing line = line[:-1] would incorrectly strip off the last character of the line.

The most elegant way to solve this problem would be to define a generator which took the lines of the file and removed the last character from each line only if that character is a newline:

def strip_trailing_newlines(file):
    for line in file:
        if line[-1] == 'n':
            yield line[:-1]
        else:
            yield line

f = open("myFile.txt", "r")
for line in strip_trailing_newlines(f):
    # do something with line

Answered By: Adam Rosenfield

Answer 2

Simple. Use splitlines()

L = open("myFile.txt", "r").read().splitlines();
for line in L: 
    process(line) # this 'line' will not have 'n' character at the end

Answered By: Vijay Dev

Answer 3

You may also consider using line.rstrip() to remove the whitespaces at the end of your line.

Answered By: Martin Cote

Answer 4

The idiomatic way to do this in Python is to use rstrip(‘n’):

for line in open('myfile.txt'):  # opened in text-mode; all EOLs are converted to 'n'
    line = line.rstrip('n')
    process(line)

Each of the other alternatives has a gotcha:

file(‘…’).read().splitlines() has to load the whole file in memory at once.
line = line[:-1] will fail if the last line has no EOL.

Answered By: efotinis

Answer 5

Long time ago, there was Dear, clean, old, BASIC code that could run on 16 kb core machines:
like that:

if (not open(1,"file.txt")) error "Could not open 'file.txt' for reading"
while(not eof(1)) 
  line input #1 a$
  print a$
wend
close

Now, to read a file line by line, with far better hardware and software (Python), we must reinvent the wheel:

def line_input (file):
    for line in file:
        if line[-1] == 'n':
            yield line[:-1]
        else:
            yield line

f = open("myFile.txt", "r")
for line_input(f):
    # do something with line

I am induced to think that something has gone the wrong way somewhere…

Answered By: Old_RattleSnake

Answer 6

What do you thing about this approach?

with open(filename) as data:
    datalines = (line.rstrip('rn') for line in data)
    for line in datalines:
        ...do something awesome...

Generator expression avoids loading whole file into memory and with ensures closing the file

Answered By: Paweł Prażak

End-line characters from lines read from text file, using Python

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