CODEWITHSUNDEEP
python
pythonquick
pythonquick

Reputation: 10869

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

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?

Upvotes: 36

Views: 128205

Answers (6)

Paweł Prażak
Paweł Prażak

Reputation: 3191

What do you thing about this approach?

with open(filename) as data:
    datalines = (line.rstrip('\r\n') 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

Upvotes: 3

Old_RattleSnake
Old_RattleSnake

Reputation:

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...

Upvotes: 5

efotinis
efotinis

Reputation: 14961

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.

Upvotes: 54

Martin Cote
Martin Cote

Reputation: 29872

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

Upvotes: 2

Vijay Dev
Vijay Dev

Reputation: 27486

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

Upvotes: 17

Adam Rosenfield
Adam Rosenfield

Reputation: 400492

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

Upvotes: 6

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