CODEWITHSUNDEEP
python
TheWiz
TheWiz

Reputation: 41

Python - Write to file is written as one long line ['text\n...text\n...'] - need to have it as the original

I`m reading a log file which has several lines and write it to a text file. the output is written to the file as one long line : ['\Bla Bla Bla\n Bla Bla Bla\n'] In original file it looks OK line by line. The reading is done like that:

text_file = open('my_file.log', 'rb')
lines = text_file.readlines()
    lines = lines[100:150] #line numbers range
    x = open(r"LocalLogFile.txt", "a")
    x.write(lines)

Any ideas how to solve it so it will look like original file?

Upvotes: 1

Views: 701

Answers (4)

Epsi95
Epsi95

Reputation: 9047

Although other's answer valid a proper way to do this is

with open('my_file.log', 'r') as f1:
    # f is an iterator
    # so instead of reading the whole file you can
    # go to the 100th line
    # suppose you you file has thousands of line

    for _ in range(100):
        next(f1)
        
    # now that you are at 100th line
    with open('LocalLogFile.txt', 'a') as f2:
        for i in range(50):
            f2.write(f1.readline())
            # no need to do next(f1 since f1.readline() will call next automatically)

Upvotes: 0

chepner
chepner

Reputation: 531075

There are several problems here:

  1. Opening a text file in binary mode
  2. Reading the entire file into memory
  3. Trying to write a list to the new file instead of a number of individual lines.

Use itertools.islice to create a new iterator that skips the first 100 lines, then yields the next 400 lines, which you can iterate over using an ordinary for loop to write to the output file.

from itertools import islice


with open('my_file.log', 'r') as f:
    with open('LocalLogFile.txt', 'a') as x:
        for line in islice(f, 100, 150):
            print(line, file=x, end='')

Some might prefer a single with statement:

with open('my_file.log', 'r') as f, open('LocalLogFile.txt', 'a') as x:
    for line in islice(f, 100, 150):
        print(line, file=x, end='')

or

with open('my_file.log', 'r') as f, \
     open('LocalLogFile.txt', 'a') as x:
    for line in islice(f, 100, 150):
        print(line, file=x, end='')

Python 3.10 will make it possible to parenthesize multiple context managers, allowing you to use multiple lines without explicit line continuation:

with (
    open('my_file.log', 'r') as f,
    open('LocalLogFile.txt', 'a') as x
):
    for line in islice(f, 100, 150):
        print(line, file=x, end='')

Upvotes: 2

AKX
AKX

Reputation: 168913

You'd need to write out each line, not the Python representation of a list.

Also, use with to manage files.

with open('my_file.log', 'rb') as text_file:
    lines = list(text_file)  # same as readlines

lines = lines[100:150]

with open("LocalLogFile.txt", "a") as x:
    x.write("".join(lines))

Upvotes: 2

Joran Beasley
Joran Beasley

Reputation: 113948

x.write(''.join(lines))

you are currently writing it as a representation of an array... but you need to write it as a string

Upvotes: -1

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