How to pick every 10 lines from a txt file using python?

Question

I need to write a code where I have huge 7000+ lines of text file. I need to split every 10lines and write it to another file.

Answer 1

Open the files, then iterate through the input lines writing every 10th line to the output file:

with open(in_name, 'r') as f:
    with open(out_name, 'w') as g:
        count = 0
        for line in f:
            if count % 10 == 0:
                g.write(line)
            count += 1

The open() context manager will close the files when the scope is exited.

Since the decision to output is simply counting you could use a slice f.readlines()[::10] although if the file is big the itertools islice generator might be more apropriate.

from itertools import islice

with open(in_name, 'r') as f:
    with open(out_name, 'w') as g:
        g.writelines( islice(f, 0, None, 10) ):

I read your question as wanting to write every 10th line. If you want to write lots of files containing 10 chunks of the file you'll need to loop until the input file is exhausted. This is not the same as the question that is shown as a duplicate. That answer breaks if the chunking reads past the end of the file.

from itertools import islice, count

out_name = 'chunk_{}.txt'

with open(in_name) as f:
    for c in count():
        chunk = list(islice(f, 10))
        if not chunk:
            break
        with open(out_name.format(c)) as g:
            g.writelines(chunk)

Answer 2

with open(fname) as f:
    content = f.readlines()
    with open(fname) as g:
        len_f = len(content)
        for x in xrange(0, len_f):
            if x % 10 = 0:
                g.write(content[x])
                g.write("\n") #For new-line
            else:
                pass
        g.close()
    f.close()

Should work! (Python 2.x)

Key take-aways:

1) Don't open / close the write-file after writing each line.

2) Close the files upon completion.