How to start reading from certain line?

Question

I'm unable to solve how can I open file for reading & writing from line 7 and to ignore everything above that line.

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2013-11-15
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I did tried the method described here: python - Read file from and to specific lines of text

but it searches for specific match and includes the text above that line. I need the reverse, to include everything starting from line 7.

I want to read everything starting from line 7 and to ignore all the previous lines [1-6] — HexSFd, Nov 15 '13 at 18:14
Right. So open the file, read the first six lines and throw them away, and then start whatever you were going to do with the rest. — Mark Reed, Nov 15 '13 at 18:22
I think you misunderstood Mark Reed. How do you mean "ignore"? I guess you want to do something with line 7 after reading it. So you can only read and then ignore lines 1-6, and finally read and do something with line 7. — leeladam, Nov 15 '13 at 18:22

jramirez · Accepted Answer · 2013-11-15T18:32:20.087

2

This will ignore the first 6 lines then print all the lines from the 7th on.

with open( file.txt, 'r') as f:
     for i, line in enumerate(f.readlines(), 0):
          if i >= 6:
              print line

or as @Paco suggested:

with open( file.txt, 'r') as f:
     for line in f.readlines()[6:]:
          print line

edited Nov 15 '13 at 18:32

answered Nov 15 '13 at 18:22

jramirez

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you should not have to read all the lines into a list with `readlines`. – iruvar Nov 15 '13 at 18:28
hint : [itertools.islice](http://docs.python.org/2/library/itertools.html#itertools.islice) – iruvar Nov 15 '13 at 18:34
1

There is no reason to read the entire file into memory. That is so unPythonic! – Nov 16 '13 at 23:37

dawg · Answer 2 · 2013-11-15T18:43:42.677

You can do this:

First create a demo file:

# create a test file of 'Line X of Y' type
with open('/tmp/lines.txt', 'w') as fout:      
    start,stop=1,11
    for i in range(start,stop):
        fout.write('Line {} of {}\n'.format(i, stop-start))

Now work with the file line-by-line:

with open('/tmp/lines.txt') as fin:
    # skip first N lines:
    N=7
    garbage=[next(fin) for i in range(N)]   
    for line in fin:
        # do what you are going to do...

You can also use itertools.islice:

import itertools        
with open('/tmp/lines.txt') as fin:
    for line in itertools.islice(fin,7,None):
        # there you go with the rest of the file...

How to start reading from certain line?

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