How to remove empty lines with or without whitespace in Python

Question

I have large string which I split by newlines. How can I remove all lines that are empty, (whitespace only)?

pseudo code:

for stuff in largestring:
   remove stuff that is blank

[For myself, I found the answer here is the best solution](http://stackoverflow.com/questions/1140958/whats-a-quick-one-liner-to-remove-empty-lines-from-a-python-string#answer-24172715) — Dmitriy, Oct 05 '16 at 06:00
One liner to remove empty lines (without whitespace) is [this](http://stackoverflow.com/a/1140966/2373278) . Question headline could potentially be changed to 'Remove empty lines with whitespace only in python'. — ViFI, Nov 03 '16 at 06:41

score 71 · Answer 1 · edited May 10 '23 at 17:06

71

Try list comprehension and string.strip():

>>> mystr = "L1\nL2\n\nL3\nL4\n  \n\nL5"
>>> mystr.split('\n')
['L1', 'L2', '', 'L3', 'L4', '  ', '', 'L5']
>>> [line for line in mystr.split('\n') if line.strip()]
['L1', 'L2', 'L3', 'L4', 'L5']

edited May 10 '23 at 17:06

Gilles Quénot

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answered Sep 14 '10 at 18:45

gimel

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you can shorten it by omitting the != '' simply "if line.strip()" – WestCoastProjects Jun 17 '13 at 21:38

NullUserException · Accepted Answer · 2010-09-14T18:48:58.477

52

Using regex:

if re.match(r'^\s*$', line):
    # line is empty (has only the following: \t\n\r and whitespace)

Using regex + filter():

filtered = filter(lambda x: not re.match(r'^\s*$', x), original)

As seen on codepad.

edited Sep 14 '10 at 18:48

answered Sep 14 '10 at 18:38

NullUserException

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Thanks for all the results, however, this solution was exactly what I had been looking for! Thanks a lot – Sep 14 '10 at 19:01
5

gimel's solution, with re-joining the text afterwards, gives a far better performance. I compared the two solutions on a small text (10 lines if which 3 were blank). Here are the results: regex: `1000 loops, best of 3: 452 us per loop`; join, split & strip: `100000 loops, best of 3: 5.41 us per loop` – m01 May 28 '13 at 08:48
Introductory video: [Python Tutorial: re Module - How to Write and Match Regular Expressions (Regex) - YouTube](https://www.youtube.com/watch?v=K8L6KVGG-7o) – Ooker Aug 23 '19 at 13:28

score 26 · Answer 3 · answered Jul 12 '13 at 08:24

26

I also tried regexp and list solutions, and list one is faster.

Here is my solution (by previous answers):

text = "\n".join([ll.rstrip() for ll in original_text.splitlines() if ll.strip()])

answered Jul 12 '13 at 08:24

Regisz

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nmichaels · Answer 4 · 2020-06-23T13:58:59.520

13

lines = bigstring.split('\n')
lines = [line for line in lines if line.strip()]

edited Jun 23 '20 at 13:58

answered Sep 14 '10 at 18:45

nmichaels

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That would work for lines = ['Line\n', '\n', 'Line\n'] but the input is 'Line\n\nLine\n' . – Walter Nissen Sep 14 '10 at 18:54
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@Walter: Actually, if you used 'Line\n\nLine\n'.split() like you should have, it would work just fine. – nmichaels Sep 14 '10 at 19:42
1

Works for me with `bigstring.split('\n')` – Hritik Dec 31 '18 at 18:18
This isn't at all what OP asks for. Try it with "a b c": it returns "a\nb\nc". – Clément Jun 22 '20 at 02:58

score 8 · Answer 5 · answered May 17 '18 at 18:45

8

Surprised a multiline re.sub has not been suggested (Oh, because you've already split your string... But why?):

>>> import re
>>> a = "Foo\n \nBar\nBaz\n\n   Garply\n  \n"
>>> print a
Foo

Bar
Baz

        Garply


>>> print(re.sub(r'\n\s*\n','\n',a,re.MULTILINE))
Foo
Bar
Baz
        Garply

>>>

answered May 17 '18 at 18:45

mushuweasel

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On a multiline sub, \s* will match any number of \n and any other whitespace: > >>> import re > >>> a = "foo\n \n\t\n \nbar\n\n \n baz" > >>> print(re.sub(r'\n\s*\n','\n',a,re.MULTILINE)) > foo > bar > baz grumble. I apparently can't figure out markdown in comments. – mushuweasel Aug 13 '19 at 21:17

Ooker · Answer 6 · 2019-08-23T13:27:14.687

3

If you are not willing to try regex (which you should), you can use this:

s.replace('\n\n','\n')

Repeat this several times to make sure there is no blank line left. Or chaining the commands:

s.replace('\n\n','\n').replace('\n\n','\n')

_{Just to encourage you to use regex, here are two introductory videos that I find intuitive:

• Regular Expressions (Regex) Tutorial

• Python Tutorial: re Module}

edited Aug 23 '19 at 13:27

answered Sep 01 '15 at 17:54

Ooker

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You may want to use a regular expression, for example. "Repeat several lines to be sure" is not a good idea when you are coding, as you may leave things unsolved or waste time running something more times than needed. – Enrico Jun 21 '16 at 04:55
+1 to regex, but as a lazy hack (or if importing the regex module is too slow) you can chain replace statements: `s.replace('\n\n','\n').replace('\n\n','\n')` Tested on 3.6. – evan_b Jun 16 '17 at 05:28
@evan_b didn't think of chaining commands. Which one will be executed first? – Ooker Jun 16 '17 at 15:03
1

Execution order appears to be left to right, but I wasn't able to find that documented anywhere after searching briefly, so it may not be safe to rely on that for order-sensitive replacements. – evan_b Jun 17 '17 at 22:53

score 2 · Answer 7 · answered Apr 11 '19 at 10:27

2

you can simply use rstrip:

    for stuff in largestring:
        print(stuff.rstrip("\n")

answered Apr 11 '19 at 10:27

Rahul Pandey

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score 1 · Answer 8 · edited Jul 22 '20 at 06:41

1

I use this solution to delete empty lines and join everything together as one line:

match_p = re.sub(r'\s{2}', '', my_txt) # my_txt is text above

edited Jul 22 '20 at 06:41

Cody Gray - on strike

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answered Nov 22 '18 at 13:26

red fred

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score 0 · Answer 9 · answered Sep 10 '15 at 12:49

0

My version:

while '' in all_lines:
    all_lines.pop(all_lines.index(''))

answered Sep 10 '15 at 12:49

Radren

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score 0 · Answer 10 · answered Jul 07 '21 at 10:06

0

Use positive lookbehind regex:

re.sub(r'(?<=\n)\s+', '', s, re.MULTILINE)

When you input:

foo
<tab> <tab>

bar

The output will be:

foo
bar

answered Jul 07 '21 at 10:06

Kxrr

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This doesn't work on first line of the file :( – Martin Jun 20 '22 at 10:18

score 0 · Answer 11 · edited Dec 16 '21 at 22:34

0

str_whith_space = """
    example line 1

    example line 2
    example line 3

    example line 4"""

new_str = '\n'.join(el.strip() for el in str_whith_space.split('\n') if el.strip())
print(new_str)

Output:

""" <br>
example line 1 <br>
example line 2 <br>
example line 3 <br>
example line 4 <br>
"""

edited Dec 16 '21 at 22:34

Patrick

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answered Dec 16 '21 at 05:53

Павел Гоняев

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score 0 · Answer 12 · answered Jul 19 '23 at 12:11

You can combine map and strip to remove spaces and use filter(None, iterable) to remove empty elements:

string = "a\n \n\nb"
list_of_str = string.split("\n")
list_of_str = filter(None, map(str.strip, list_of_str))
list(list_of_str)

Returns: ['a', 'b']

score -1 · Answer 13 · answered May 24 '17 at 19:07

-1

Same as what @NullUserException said, this is how I write it:

removedWhitespce = re.sub(r'^\s*$', '', line)

answered May 24 '17 at 19:07

Reihan_amn

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How to remove empty lines with or without whitespace in Python

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