Reputation: 569
I would like to copy certain lines of text from one text file to another. In my current script when I search for a string it copies everything afterwards, how can I copy just a certain part of the text? E.g. only copy lines when it has "tests/file/myword" in it?
current code:
#!/usr/bin/env python
f = open('list1.txt')
f1 = open('output.txt', 'a')
doIHaveToCopyTheLine=False
for line in f.readlines():
if 'tests/file/myword' in line:
doIHaveToCopyTheLine=True
if doIHaveToCopyTheLine:
f1.write(line)
f1.close()
f.close()
Upvotes: 42
Views: 213613
Reputation: 27486
in Python 3.10
with parenthesized context managers, you can use multiple context managers in one with block:
with (open('list1.txt', 'w') as fout, open('output.txt') as fin):
fout.write(fin.read())
Upvotes: 2
Reputation: 29
f=open('list1.txt')
f1=open('output.txt','a')
for x in f.readlines():
f1.write(x)
f.close()
f1.close()
this will work 100% try this once
Upvotes: 2
Reputation: 140316
Safe and memory-saving:
with open("out1.txt", "w") as fw, open("in.txt","r") as fr:
fw.writelines(l for l in fr if "tests/file/myword" in l)
It doesn't create temporary lists (what readline
and []
would do, which is a non-starter if the file is huge), all is done with generator comprehensions, and using with
blocks ensure that the files are closed on exit.
Upvotes: 8
Reputation: 17
f = open('list1.txt')
f1 = open('output.txt', 'a')
# doIHaveToCopyTheLine=False
for line in f.readlines():
if 'tests/file/myword' in line:
f1.write(line)
f1.close()
f.close()
Now Your code will work. Try This one.
Upvotes: -2
Reputation: 4574
Just a slightly cleaned up way of doing this. This is no more or less performant than ATOzTOA's answer, but there's no reason to do two separate with statements.
with open(path_1, 'a') as file_1, open(path_2, 'r') as file_2:
for line in file_2:
if 'tests/file/myword' in line:
file_1.write(line)
Upvotes: 9
Reputation: 36000
The oneliner:
open("out1.txt", "w").writelines([l for l in open("in.txt").readlines() if "tests/file/myword" in l])
Recommended with with
:
with open("in.txt") as f:
lines = f.readlines()
lines = [l for l in lines if "ROW" in l]
with open("out.txt", "w") as f1:
f1.writelines(lines)
Using less memory:
with open("in.txt") as f:
with open("out.txt", "w") as f1:
for line in f:
if "ROW" in line:
f1.write(line)
Upvotes: 86
Reputation: 77407
readlines() reads the entire input file into a list and is not a good performer. Just iterate through the lines in the file. I used 'with' on output.txt so that it is automatically closed when done. That's not needed on 'list1.txt' because it will be closed when the for loop ends.
#!/usr/bin/env python
with open('output.txt', 'a') as f1:
for line in open('list1.txt'):
if 'tests/file/myword' in line:
f1.write(line)
Upvotes: 11