Python: read all text file lines in loop
PythonFilePython Problem Overview
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
Python Solutions
Solution 1 - Python
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
> 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.
Solution 2 - Python
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
Solution 3 - Python
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.
Solution 4 - Python
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