Python: read all text file lines in loop

Question

I want to read huge text file line by line (and stop if a line with “str” found).
How to check, if file-end is reached?

fn = 't.log'
f = open(fn, 'r')
while not _is_eof(f): ## how to check that end is reached?
    s = f.readline()
    print s
    if "str" in s: break

Asked By: Prog1020

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Source

Answer 1

Just iterate over each line in the file. Python automatically checks for the End of file and closes the file for you (using the with syntax).

with open('fileName', 'r') as f:
    for line in f:
       if 'str' in line:
           break

Answered By: Sukrit Kalra

Answer 2

There’s no need to check for EOF in python, simply do:

with open('t.ini') as f:
   for line in f:
       # For Python3, use print(line)
       print line
       if 'str' in line:
          break

Why the with statement:

It is good practice to use the with keyword when dealing with file
objects. This has the advantage that the file is properly closed after
its suite finishes, even if an exception is raised on the way.

Answered By: Ashwini Chaudhary

Answer 3

There are situations where you can’t use the (quite convincing) with... for... structure. In that case, do the following:

line = self.fo.readline()
if len(line) != 0:
     if 'str' in line:
         break

This will work because the the readline() leaves a trailing newline character, where as EOF is just an empty string.

Answered By: Damian Vogel

Answer 4

You can stop the 2-line separation in the output by using

    with open('t.ini') as f:
       for line in f:
           print line.strip()
           if 'str' in line:
              break

Answered By: Chris

Python: read all text file lines in loop

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