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Regular Expression '[w-]+(.[w-]+)*' doesn't get matched

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1

I want to process some sentences in the document of PostgreSQL and do some analysis. In the word spliting stage, I tried to use the regex '[w-]+(.[w-]+)*' proposed by Lotufo et al. in the article Modelling the Hurried bug report reading process to summarize
bug reports. It's quite strange that I cann't get the expected answer using this regex in Python.

Python 3.6.5 |Anaconda, Inc.| (default, Mar 29 2018, 13:32:41) [MSC v.1900 64 bit (AMD64)]
Type "copyright", "credits" or "license" for more information.

IPython 6.4.0 -- An enhanced Interactive Python.
>>> import re
>>> result = re.findall(r'[w-]+(.[w-]+)*', 'Specifies the directory to use for data storage.')
>>> print(result)

I expected to get a list of words：

['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']

But I only got a list of empty string:

['', '', '', '', '', '', '', '']

Does any one have any idea what is wrong with my code? Thanks a lot.

regex python-3.x

share|improve this question

edited Mar 25 at 0:26

Chanlen

asked Mar 23 at 3:11

ChanlenChanlen

235

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use string.split(' ') to segment the sentence, it's easy to understand and improve runtime efficiency.
  
  – pandalai
  Mar 23 at 5:48
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This regex has special meaning in spliting the computer words. The function string.split(' ') may work well on the above sentence but for certain sentences it cannot reach the aim of spliting.
  
  – Chanlen
  Mar 23 at 8:03
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Chanlen, could you please post a better explanation of what are you trying to accomplish with that regex? More examples of right and wrong input/outputs would be great.
  
  – accdias
  Mar 23 at 23:05
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Sorry for making it confused. I have re-edited the post and it should be more clear.
  
  – Chanlen
  Mar 25 at 0:31
  
  

  
  
  
  

add a comment | 

1

I want to process some sentences in the document of PostgreSQL and do some analysis. In the word spliting stage, I tried to use the regex '[w-]+(.[w-]+)*' proposed by Lotufo et al. in the article Modelling the Hurried bug report reading process to summarize
bug reports. It's quite strange that I cann't get the expected answer using this regex in Python.

Python 3.6.5 |Anaconda, Inc.| (default, Mar 29 2018, 13:32:41) [MSC v.1900 64 bit (AMD64)]
Type "copyright", "credits" or "license" for more information.

IPython 6.4.0 -- An enhanced Interactive Python.
>>> import re
>>> result = re.findall(r'[w-]+(.[w-]+)*', 'Specifies the directory to use for data storage.')
>>> print(result)

I expected to get a list of words：

['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']

But I only got a list of empty string:

['', '', '', '', '', '', '', '']

Does any one have any idea what is wrong with my code? Thanks a lot.

regex python-3.x

share|improve this question

edited Mar 25 at 0:26

Chanlen

asked Mar 23 at 3:11

ChanlenChanlen

235

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use string.split(' ') to segment the sentence, it's easy to understand and improve runtime efficiency.
  
  – pandalai
  Mar 23 at 5:48
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This regex has special meaning in spliting the computer words. The function string.split(' ') may work well on the above sentence but for certain sentences it cannot reach the aim of spliting.
  
  – Chanlen
  Mar 23 at 8:03
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Chanlen, could you please post a better explanation of what are you trying to accomplish with that regex? More examples of right and wrong input/outputs would be great.
  
  – accdias
  Mar 23 at 23:05
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Sorry for making it confused. I have re-edited the post and it should be more clear.
  
  – Chanlen
  Mar 25 at 0:31
  
  

  
  
  
  

add a comment | 

I want to process some sentences in the document of PostgreSQL and do some analysis. In the word spliting stage, I tried to use the regex '[w-]+(.[w-]+)*' proposed by Lotufo et al. in the article Modelling the Hurried bug report reading process to summarize
bug reports. It's quite strange that I cann't get the expected answer using this regex in Python.

Python 3.6.5 |Anaconda, Inc.| (default, Mar 29 2018, 13:32:41) [MSC v.1900 64 bit (AMD64)]
Type "copyright", "credits" or "license" for more information.

IPython 6.4.0 -- An enhanced Interactive Python.
>>> import re
>>> result = re.findall(r'[w-]+(.[w-]+)*', 'Specifies the directory to use for data storage.')
>>> print(result)

I expected to get a list of words：

['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']

But I only got a list of empty string:

['', '', '', '', '', '', '', '']

Does any one have any idea what is wrong with my code? Thanks a lot.

regex python-3.x

share|improve this question

edited Mar 25 at 0:26

Chanlen

asked Mar 23 at 3:11

ChanlenChanlen

235

Python 3.6.5 |Anaconda, Inc.| (default, Mar 29 2018, 13:32:41) [MSC v.1900 64 bit (AMD64)]
Type "copyright", "credits" or "license" for more information.

IPython 6.4.0 -- An enhanced Interactive Python.
>>> import re
>>> result = re.findall(r'[w-]+(.[w-]+)*', 'Specifies the directory to use for data storage.')
>>> print(result)

['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']

['', '', '', '', '', '', '', '']

share|improve this question

edited Mar 25 at 0:26

Chanlen

asked Mar 23 at 3:11

ChanlenChanlen

235

share|improve this question

edited Mar 25 at 0:26

Chanlen

asked Mar 23 at 3:11

ChanlenChanlen

235

asked Mar 23 at 3:11

ChanlenChanlen

235

asked Mar 23 at 3:11

ChanlenChanlen

235

2 Answers
2

active

oldest

votes

0

This works the way you were expecting:

Python 3.7.2 (default, Jan 16 2019, 19:49:22) 
[GCC 8.2.1 20181215 (Red Hat 8.2.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> split = re.compile('(w+)')
>>> split.findall('Specifies the directory to use for data storage.')
['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']
>>> 

Those square brackets on your regular expression don't feel right. I guess they are the cause.

share|improve this answer

edited Mar 23 at 21:33

answered Mar 23 at 21:22

accdiasaccdias

868714

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This regex is not equivalent to the original one. The regex is supposed to allow dots (except at the beginning and at the end of a word)
  
  – Aloso
  Mar 23 at 22:54
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the explanation @Aloso, but yours will allow a string like one.two being matched as a one single word. Is that the right thing?
  
  – accdias
  Mar 23 at 23:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Apparently it is. Just look at the regex [w-]+(.[w-]+)*. We don't know what @Chanlen needs it for, so let's not jump to any conclusions.
  
  – Aloso
  Mar 23 at 23:08
  

  
  
  
  

add a comment | 

0

The expected strings are matched, but they aren't in a capturing group. Use this regex instead:

r'([w-]+(?:.[w-]+)*)'

Note that I added ?: to the inner parentheses to make them non-capturing.

share|improve this answer

answered Mar 23 at 22:51

AlosoAloso

1,94131728

add a comment | 

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0

This works the way you were expecting:

Python 3.7.2 (default, Jan 16 2019, 19:49:22) 
[GCC 8.2.1 20181215 (Red Hat 8.2.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> split = re.compile('(w+)')
>>> split.findall('Specifies the directory to use for data storage.')
['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']
>>> 

Those square brackets on your regular expression don't feel right. I guess they are the cause.

share|improve this answer

edited Mar 23 at 21:33

answered Mar 23 at 21:22

accdiasaccdias

868714

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This regex is not equivalent to the original one. The regex is supposed to allow dots (except at the beginning and at the end of a word)
  
  – Aloso
  Mar 23 at 22:54
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the explanation @Aloso, but yours will allow a string like one.two being matched as a one single word. Is that the right thing?
  
  – accdias
  Mar 23 at 23:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Apparently it is. Just look at the regex [w-]+(.[w-]+)*. We don't know what @Chanlen needs it for, so let's not jump to any conclusions.
  
  – Aloso
  Mar 23 at 23:08
  

  
  
  
  

add a comment | 

0

This works the way you were expecting:

Python 3.7.2 (default, Jan 16 2019, 19:49:22) 
[GCC 8.2.1 20181215 (Red Hat 8.2.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> split = re.compile('(w+)')
>>> split.findall('Specifies the directory to use for data storage.')
['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']
>>> 

Those square brackets on your regular expression don't feel right. I guess they are the cause.

share|improve this answer

edited Mar 23 at 21:33

answered Mar 23 at 21:22

accdiasaccdias

868714

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This regex is not equivalent to the original one. The regex is supposed to allow dots (except at the beginning and at the end of a word)
  
  – Aloso
  Mar 23 at 22:54
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the explanation @Aloso, but yours will allow a string like one.two being matched as a one single word. Is that the right thing?
  
  – accdias
  Mar 23 at 23:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Apparently it is. Just look at the regex [w-]+(.[w-]+)*. We don't know what @Chanlen needs it for, so let's not jump to any conclusions.
  
  – Aloso
  Mar 23 at 23:08
  

  
  
  
  

add a comment | 

This works the way you were expecting:

Python 3.7.2 (default, Jan 16 2019, 19:49:22) 
[GCC 8.2.1 20181215 (Red Hat 8.2.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> split = re.compile('(w+)')
>>> split.findall('Specifies the directory to use for data storage.')
['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']
>>> 

Those square brackets on your regular expression don't feel right. I guess they are the cause.

share|improve this answer

edited Mar 23 at 21:33

answered Mar 23 at 21:22

accdiasaccdias

868714

Python 3.7.2 (default, Jan 16 2019, 19:49:22) 
[GCC 8.2.1 20181215 (Red Hat 8.2.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> split = re.compile('(w+)')
>>> split.findall('Specifies the directory to use for data storage.')
['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']
>>> 

share|improve this answer

edited Mar 23 at 21:33

answered Mar 23 at 21:22

accdiasaccdias

868714

answered Mar 23 at 21:22

accdiasaccdias

868714

answered Mar 23 at 21:22

accdiasaccdias

868714

0

The expected strings are matched, but they aren't in a capturing group. Use this regex instead:

r'([w-]+(?:.[w-]+)*)'

Note that I added ?: to the inner parentheses to make them non-capturing.

share|improve this answer

answered Mar 23 at 22:51

AlosoAloso

1,94131728

add a comment | 

0

The expected strings are matched, but they aren't in a capturing group. Use this regex instead:

r'([w-]+(?:.[w-]+)*)'

Note that I added ?: to the inner parentheses to make them non-capturing.

share|improve this answer

answered Mar 23 at 22:51

AlosoAloso

1,94131728

add a comment | 

The expected strings are matched, but they aren't in a capturing group. Use this regex instead:

r'([w-]+(?:.[w-]+)*)'

Note that I added ?: to the inner parentheses to make them non-capturing.

share|improve this answer

answered Mar 23 at 22:51

AlosoAloso

1,94131728

r'([w-]+(?:.[w-]+)*)'

share|improve this answer

answered Mar 23 at 22:51

AlosoAloso

1,94131728

answered Mar 23 at 22:51

AlosoAloso

1,94131728

answered Mar 23 at 22:51

AlosoAloso

1,94131728