Reading values of two lines and write in one line with python

Question

I have a file with this format:

611    2856     618    2582   94075   94107   94065   94068
101071   94104
598    2856     618     611   93995   94107   93992   93991
94075   94065
612    2834    2821    2812   94087  101577   94085   94081
101558  101557

I need to read the lines and to rewrite them so:

611    2856     618    2582   94075   94107   94065   94068 101071   94104
598    2856     618     611   93995   94107   93992   93991 94075   94065
612    2834    2821    2812   94087  101577   94085   94081 101558  101557

I have tried something like this:

f2 = open('new_file.txt', 'w')
    f1 = open('old_file.txt')
    lines = f1.readlines()
    for i, line in enumerate(lines):    
        print(repr(line))               
        f2.write(line)
        i = i+1
    f1.close()
f2.close()

But it is not working as it writes again every line. I need to read two lines and write them in one. Any suggesitons?

PM 2Ring · Accepted Answer · 2017-01-24T13:29:00.573

You don't need to read the lines into a list, or mess about with line numbers, you can just iterate directly over the file lines:

with open('oldfile.txt') as fin, open('newfile.txt', 'w') as fout:
    for line in fin:
        fout.write(line[:-1] + ' ' + next(fin))

contents of newfile.txt

611    2856     618    2582   94075   94107   94065   94068 101071   94104
598    2856     618     611   93995   94107   93992   93991 94075   94065
612    2834    2821    2812   94087  101577   94085   94081 101558  101557

line[:-1] + ' '

removes the newline char at the end of the long lines, and replaces it with a single space; I'm pretty sure that this is faster than doing line.replace('\n', ' '), but I haven't timed it.

As with Graipher's solution, if the file doesn't have an even number of lines, then the last line will not be copied, but I assume that's not an issue for your data.

score 1 · Answer 2 · edited May 23 '17 at 12:01

The lines returned by readlines still contain the newline '\n' at the end. You must strip them:

with open('new_file.txt', 'w') as f2:
    with open('old_file.txt') as f1:
        lines = f1.readlines()
        # lines = f1.read().splitlines()  will even save you the stripping
        for i, line in enumerate(lines):  # line: 'foo bar \n'         
            f2.write(line.strip())
            if i % 2:  # linebreak only every other line
                f2.write('\n')

score 1 · Answer 3 · answered Jan 24 '17 at 13:09

You can use a buffer variable to store every second line like so:

with open('new_file.txt', 'w') as fout:
    with open('old_file.txt') as fin:
        buffer = ""
        for i, line in enumerate(fin):
            if i % 2 == 0:
                buffer = line.replace('\n', '')
            else:
                fout.write(sep.join((buffer, line)))
                buffer = ""

With sep = " " or whatever else you use for separation.

This assumes you have an even number of lines, otherwise the last line will not be written.

Reading values of two lines and write in one line with python

3 Answers3