Python: Filter lines from a text file which contain a particular word

In Python, I want to write a program which filters the lines from my text file which contain the word "apple" and write those lines into a new text file. What I have tried just writes the word "apple" in my new text file, whereas I want whole lines. I am a beginner in Python, so kindly reply to my question, as I really need this.

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

asked Mar 9 '11 at 11:22

ahmad

59113

add a comment |

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

asked Mar 9 '11 at 11:22

ahmad

59113

add a comment |

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

asked Mar 9 '11 at 11:22

ahmad

59113

python filter line

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

asked Mar 9 '11 at 11:22

ahmad

59113

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

asked Mar 9 '11 at 11:22

ahmad

59113

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

edited Mar 17 '11 at 3:17

Josh Caswell

59.2k12130176

asked Mar 9 '11 at 11:22

ahmad

59113

asked Mar 9 '11 at 11:22

ahmad

59113

asked Mar 9 '11 at 11:22

ahmad

59113

add a comment |

5 Answers
5

active

oldest

votes

Use can get all lines containing 'apple' using a list-comprehension:

[ line for line in open('textfile') if 'apple' in line]

So - also in one code-line - you can create the new textfile:

open('newfile','w').writelines([ line for line in open('textfile') if 'apple' in line])

And eyquem is right: it's definitely faster to keep it as an iterator and write

open('newfile','w').writelines(line for line in open('textfile') if 'apple' in line)

edited May 3 '17 at 20:27

answered Mar 9 '11 at 11:37

phynfo

3,06211436

4

A list comprehension creates an object. Using a generator expression would be better. By the way it can be written writelines( line for line in open('textfile') if 'apple' in line)

– eyquem
Mar 9 '11 at 12:03

@eyquem: Ok, I totally agree that -- for large files -- it should be the better to use generators, since a generator behaves lazily and thus doesnt consume that much memory. But probably for small files the list-comprehension is the faster solution?

– phynfo
Mar 9 '11 at 12:23

@Phynfo: Nope... keeping things as generators/iterators is far more efficient. The list comprehension is still creating the iterator, which is then filling a list, and once complete passing that list to writelines which turns it back into an iterator.

– Chris Cogdon
Nov 4 '15 at 0:46

Can I use multiple strings here to match? Ex: I want to retain only line with string 'apple' or 'orange'

– Gajendra D Ambi
Apr 26 '17 at 8:13

You can replace if 'apple' in line with if 'apple' in line or 'orange' in line

– phynfo
May 3 '17 at 20:24

add a comment |

from itertools import ifilter



with open('source.txt','rb') as f,open('new.txt','wb') as g:



    g.writelines( ifilter(lambda line: 'apple' in line, f))

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

add a comment |

Using generators, this is memory efficient and fast

def apple_finder(file):

    for line in file:

        if 'apple' in line:

             yield line





source = open('forest','rb')



apples = apple_finder(source)

I love easy solutions with no brain damage for reading :-)

answered Mar 9 '11 at 12:07

Mario César

2,25621937

1

The function apple_finder(file) is a function generator and apples is a generator. The latter do the same job as ifilter(lambda line: 'apple' in line, f) in two lines (import comprised)

– eyquem
Mar 9 '11 at 12:39

add a comment |

if "apple" in line: should work.

answered Mar 9 '11 at 11:37

neil

2,2311010

add a comment |

For Python3 - here is working and fast example

with open('input.txt', 'rb') as file_in:

    with open("output.txt", "wb") as file_out:

        file_out.writelines(filter(lambda line: b'lines with this text' in line, file_in))

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f5245058%2fpython-filter-lines-from-a-text-file-which-contain-a-particular-word%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

5 Answers
5

active

oldest

votes

5 Answers
5

active

oldest

votes

Use can get all lines containing 'apple' using a list-comprehension:

[ line for line in open('textfile') if 'apple' in line]

So - also in one code-line - you can create the new textfile:

open('newfile','w').writelines([ line for line in open('textfile') if 'apple' in line])

And eyquem is right: it's definitely faster to keep it as an iterator and write

open('newfile','w').writelines(line for line in open('textfile') if 'apple' in line)

edited May 3 '17 at 20:27

answered Mar 9 '11 at 11:37

phynfo

3,06211436

4

A list comprehension creates an object. Using a generator expression would be better. By the way it can be written writelines( line for line in open('textfile') if 'apple' in line)

– eyquem
Mar 9 '11 at 12:03

@eyquem: Ok, I totally agree that -- for large files -- it should be the better to use generators, since a generator behaves lazily and thus doesnt consume that much memory. But probably for small files the list-comprehension is the faster solution?

– phynfo
Mar 9 '11 at 12:23

@Phynfo: Nope... keeping things as generators/iterators is far more efficient. The list comprehension is still creating the iterator, which is then filling a list, and once complete passing that list to writelines which turns it back into an iterator.

– Chris Cogdon
Nov 4 '15 at 0:46

Can I use multiple strings here to match? Ex: I want to retain only line with string 'apple' or 'orange'

– Gajendra D Ambi
Apr 26 '17 at 8:13

You can replace if 'apple' in line with if 'apple' in line or 'orange' in line

– phynfo
May 3 '17 at 20:24

add a comment |

Use can get all lines containing 'apple' using a list-comprehension:

[ line for line in open('textfile') if 'apple' in line]

So - also in one code-line - you can create the new textfile:

open('newfile','w').writelines([ line for line in open('textfile') if 'apple' in line])

And eyquem is right: it's definitely faster to keep it as an iterator and write

open('newfile','w').writelines(line for line in open('textfile') if 'apple' in line)

edited May 3 '17 at 20:27

answered Mar 9 '11 at 11:37

phynfo

3,06211436

4

A list comprehension creates an object. Using a generator expression would be better. By the way it can be written writelines( line for line in open('textfile') if 'apple' in line)

– eyquem
Mar 9 '11 at 12:03

@eyquem: Ok, I totally agree that -- for large files -- it should be the better to use generators, since a generator behaves lazily and thus doesnt consume that much memory. But probably for small files the list-comprehension is the faster solution?

– phynfo
Mar 9 '11 at 12:23

@Phynfo: Nope... keeping things as generators/iterators is far more efficient. The list comprehension is still creating the iterator, which is then filling a list, and once complete passing that list to writelines which turns it back into an iterator.

– Chris Cogdon
Nov 4 '15 at 0:46

Can I use multiple strings here to match? Ex: I want to retain only line with string 'apple' or 'orange'

– Gajendra D Ambi
Apr 26 '17 at 8:13

You can replace if 'apple' in line with if 'apple' in line or 'orange' in line

– phynfo
May 3 '17 at 20:24

add a comment |

Use can get all lines containing 'apple' using a list-comprehension:

[ line for line in open('textfile') if 'apple' in line]

So - also in one code-line - you can create the new textfile:

open('newfile','w').writelines([ line for line in open('textfile') if 'apple' in line])

And eyquem is right: it's definitely faster to keep it as an iterator and write

open('newfile','w').writelines(line for line in open('textfile') if 'apple' in line)

edited May 3 '17 at 20:27

answered Mar 9 '11 at 11:37

phynfo

3,06211436

Use can get all lines containing 'apple' using a list-comprehension:

[ line for line in open('textfile') if 'apple' in line]

So - also in one code-line - you can create the new textfile:

open('newfile','w').writelines([ line for line in open('textfile') if 'apple' in line])

And eyquem is right: it's definitely faster to keep it as an iterator and write

open('newfile','w').writelines(line for line in open('textfile') if 'apple' in line)

edited May 3 '17 at 20:27

answered Mar 9 '11 at 11:37

phynfo

3,06211436

edited May 3 '17 at 20:27

answered Mar 9 '11 at 11:37

phynfo

3,06211436

answered Mar 9 '11 at 11:37

phynfo

3,06211436

answered Mar 9 '11 at 11:37

phynfo

3,06211436

4

A list comprehension creates an object. Using a generator expression would be better. By the way it can be written writelines( line for line in open('textfile') if 'apple' in line)

– eyquem
Mar 9 '11 at 12:03

@eyquem: Ok, I totally agree that -- for large files -- it should be the better to use generators, since a generator behaves lazily and thus doesnt consume that much memory. But probably for small files the list-comprehension is the faster solution?

– phynfo
Mar 9 '11 at 12:23

@Phynfo: Nope... keeping things as generators/iterators is far more efficient. The list comprehension is still creating the iterator, which is then filling a list, and once complete passing that list to writelines which turns it back into an iterator.

– Chris Cogdon
Nov 4 '15 at 0:46

Can I use multiple strings here to match? Ex: I want to retain only line with string 'apple' or 'orange'

– Gajendra D Ambi
Apr 26 '17 at 8:13

You can replace if 'apple' in line with if 'apple' in line or 'orange' in line

– phynfo
May 3 '17 at 20:24

add a comment |

4

A list comprehension creates an object. Using a generator expression would be better. By the way it can be written writelines( line for line in open('textfile') if 'apple' in line)

– eyquem
Mar 9 '11 at 12:03

@eyquem: Ok, I totally agree that -- for large files -- it should be the better to use generators, since a generator behaves lazily and thus doesnt consume that much memory. But probably for small files the list-comprehension is the faster solution?

– phynfo
Mar 9 '11 at 12:23

@Phynfo: Nope... keeping things as generators/iterators is far more efficient. The list comprehension is still creating the iterator, which is then filling a list, and once complete passing that list to writelines which turns it back into an iterator.

– Chris Cogdon
Nov 4 '15 at 0:46

Can I use multiple strings here to match? Ex: I want to retain only line with string 'apple' or 'orange'

– Gajendra D Ambi
Apr 26 '17 at 8:13

You can replace if 'apple' in line with if 'apple' in line or 'orange' in line

– phynfo
May 3 '17 at 20:24

A list comprehension creates an object. Using a generator expression would be better. By the way it can be written writelines( line for line in open('textfile') if 'apple' in line)

– eyquem
Mar 9 '11 at 12:03

@eyquem: Ok, I totally agree that -- for large files -- it should be the better to use generators, since a generator behaves lazily and thus doesnt consume that much memory. But probably for small files the list-comprehension is the faster solution?

– phynfo
Mar 9 '11 at 12:23

@Phynfo: Nope... keeping things as generators/iterators is far more efficient. The list comprehension is still creating the iterator, which is then filling a list, and once complete passing that list to writelines which turns it back into an iterator.

– Chris Cogdon
Nov 4 '15 at 0:46

Can I use multiple strings here to match? Ex: I want to retain only line with string 'apple' or 'orange'

– Gajendra D Ambi
Apr 26 '17 at 8:13

You can replace if 'apple' in line with if 'apple' in line or 'orange' in line

– phynfo
May 3 '17 at 20:24

add a comment |

from itertools import ifilter



with open('source.txt','rb') as f,open('new.txt','wb') as g:



    g.writelines( ifilter(lambda line: 'apple' in line, f))

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

add a comment |

from itertools import ifilter



with open('source.txt','rb') as f,open('new.txt','wb') as g:



    g.writelines( ifilter(lambda line: 'apple' in line, f))

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

add a comment |

from itertools import ifilter



with open('source.txt','rb') as f,open('new.txt','wb') as g:



    g.writelines( ifilter(lambda line: 'apple' in line, f))

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

from itertools import ifilter



with open('source.txt','rb') as f,open('new.txt','wb') as g:



    g.writelines( ifilter(lambda line: 'apple' in line, f))

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

answered Mar 9 '11 at 11:58

eyquem

20.1k42739

add a comment |

Using generators, this is memory efficient and fast

def apple_finder(file):

    for line in file:

        if 'apple' in line:

             yield line





source = open('forest','rb')



apples = apple_finder(source)

I love easy solutions with no brain damage for reading :-)

answered Mar 9 '11 at 12:07

Mario César

2,25621937

1

The function apple_finder(file) is a function generator and apples is a generator. The latter do the same job as ifilter(lambda line: 'apple' in line, f) in two lines (import comprised)

– eyquem
Mar 9 '11 at 12:39

add a comment |

Using generators, this is memory efficient and fast

def apple_finder(file):

    for line in file:

        if 'apple' in line:

             yield line





source = open('forest','rb')



apples = apple_finder(source)

I love easy solutions with no brain damage for reading :-)

answered Mar 9 '11 at 12:07

Mario César

2,25621937

1

The function apple_finder(file) is a function generator and apples is a generator. The latter do the same job as ifilter(lambda line: 'apple' in line, f) in two lines (import comprised)

– eyquem
Mar 9 '11 at 12:39

add a comment |

Using generators, this is memory efficient and fast

def apple_finder(file):

    for line in file:

        if 'apple' in line:

             yield line





source = open('forest','rb')



apples = apple_finder(source)

I love easy solutions with no brain damage for reading :-)

answered Mar 9 '11 at 12:07

Mario César

2,25621937

Using generators, this is memory efficient and fast

def apple_finder(file):

    for line in file:

        if 'apple' in line:

             yield line





source = open('forest','rb')



apples = apple_finder(source)

I love easy solutions with no brain damage for reading :-)

answered Mar 9 '11 at 12:07

Mario César

2,25621937

answered Mar 9 '11 at 12:07

Mario César

2,25621937

answered Mar 9 '11 at 12:07

Mario César

2,25621937

answered Mar 9 '11 at 12:07

Mario César

2,25621937

1

The function apple_finder(file) is a function generator and apples is a generator. The latter do the same job as ifilter(lambda line: 'apple' in line, f) in two lines (import comprised)

– eyquem
Mar 9 '11 at 12:39

add a comment |

1

The function apple_finder(file) is a function generator and apples is a generator. The latter do the same job as ifilter(lambda line: 'apple' in line, f) in two lines (import comprised)

– eyquem
Mar 9 '11 at 12:39

The function apple_finder(file) is a function generator and apples is a generator. The latter do the same job as ifilter(lambda line: 'apple' in line, f) in two lines (import comprised)

– eyquem
Mar 9 '11 at 12:39

add a comment |

if "apple" in line: should work.

answered Mar 9 '11 at 11:37

neil

2,2311010

add a comment |

if "apple" in line: should work.

answered Mar 9 '11 at 11:37

neil

2,2311010

add a comment |

if "apple" in line: should work.

answered Mar 9 '11 at 11:37

neil

2,2311010

if "apple" in line: should work.

answered Mar 9 '11 at 11:37

neil

2,2311010

answered Mar 9 '11 at 11:37

neil

2,2311010

answered Mar 9 '11 at 11:37

neil

2,2311010

answered Mar 9 '11 at 11:37

neil

2,2311010

add a comment |

For Python3 - here is working and fast example

with open('input.txt', 'rb') as file_in:

    with open("output.txt", "wb") as file_out:

        file_out.writelines(filter(lambda line: b'lines with this text' in line, file_in))

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

add a comment |

For Python3 - here is working and fast example

with open('input.txt', 'rb') as file_in:

    with open("output.txt", "wb") as file_out:

        file_out.writelines(filter(lambda line: b'lines with this text' in line, file_in))

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

add a comment |

For Python3 - here is working and fast example

with open('input.txt', 'rb') as file_in:

    with open("output.txt", "wb") as file_out:

        file_out.writelines(filter(lambda line: b'lines with this text' in line, file_in))

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

For Python3 - here is working and fast example

with open('input.txt', 'rb') as file_in:

    with open("output.txt", "wb") as file_out:

        file_out.writelines(filter(lambda line: b'lines with this text' in line, file_in))

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

answered Nov 25 '18 at 17:34

pbaranski

9,368116476

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Tukukkk