Read file until specific line in python

Question

I have one text file. I am parsing some data using regex. So open the file and read it and the parse it. But I don't want to read and parse data after some specific line in that text file. For example

file start here..
some data...
SPECIFIC LINE
some data....

Now I don't want to read file after SPECIFIC LINE... Is there any way to stop reading when that line reaches?

A `for` loop with a `break`? This is pretty standard ... can you show us your efforts so we can help you rather than just requesting we do it for you? — g.d.d.c, Nov 25 '14 at 19:55

score 7 · Accepted Answer · answered Nov 25 '14 at 21:19

This is pretty straight forward, you can terminate a loop early with a break statement.

filename = 'somefile.txt'

with open(filename, 'r') as input:
   for line in input:
       if 'indicator' in line:
            break

Using with creates a compound statement that ensures that upon entering and leaving the scope of the with statement __enter__() and __exit__() will be called respectively. For the purpose of file reading this will prevent any dangling filehandles.

The break statement tells the loop to terminate immediately.

Raymond · Answer 2 · 2017-01-04T04:10:59.970

4

Use iter()'s sentinel parameter:

with open('test.txt') as f:
    for line in iter(lambda: f.readline().rstrip(), 'SPECIFIC LINE'):
        print(line)

output:

file start here..
some data...

Reference: https://docs.python.org/2/library/functions.html#iter

edited Jan 04 '17 at 04:10

answered Jan 03 '17 at 07:23

Raymond

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ZygD · Answer 3 · 2021-03-31T10:23:19.423

0

Read only first n lines without loading the whole file:

n = 5
with open(r'C:\Temp\test.txt', encoding='utf8') as f:
    head = [next(f) for x in range(n)]

edited Mar 31 '21 at 10:23

answered Mar 31 '21 at 07:58

ZygD

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Read file until specific line in python

3 Answers3