splitting strings with multiple delimiters in python with re.split (from python cookbook)

Question

In Chapter 2, Section 2.1 of Python Cookbook 3rd Edition, you have the following:

>>> line = 'asdf fjdk; afed, fjek,asdf,      foo'
>>> import re
>>> re.split(r'[;,\s]\s*', line)
['asdf', 'fjdk', 'afed', 'fjek', 'asdf', 'foo']

Yes it is a nice example... but when I try it out with removing the \s* in the regex it still has the same effect... see below:

>>> re.split(r'[;,\s]*', line)
['asdf', 'fjdk', 'afed', 'fjek', 'asdf', 'foo']

So, what does the author have in mind to make the redundant \s* useful for any other purposes than doing it without.. which is more simple and shorter?

Please make ur input.

sberry · Accepted Answer · 2014-05-29 04:15:36Z

3

I don't have the book, so I don't know the authors' intent. But David Beazley is as sharp as they come so I can only guess that it was to distinguish between the output for these two lines.

>>> line = 'asdf fjdk; afed, fjek,asdf,      foo'
>>> line = 'asdf fjdk; ; afed, fjek,asdf,      foo'

Using the regex from the book, the second line would be

['asdf', 'fjdk', '', 'afed', 'fjek', 'asdf', 'foo']

And using your modified regex

['asdf', 'fjdk', 'afed', 'fjek', 'asdf', 'foo']

Your regex will collapse all of the symbols in the group [;,\s] that are not separated by a character not in the match group.

answered May 29, 2014 at 4:15

sberry

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ihightower Over a year ago

thank u for ur input.. excellent example for using the book's regex.

Abhijit · Accepted Answer · 2014-05-29 04:16:50Z

1

Both the regular expressions are different.

The first regex states that, the delimiter should either be a comma, semi-colon or a space optionally followed by spaces
The second regex states that, the delimiter should either one or more comma, semi-colon or a space.

So going by the definition, you can easily find the difference if you apply the regex on the following string

line = 'asdf fjdk;; afed, fjek,asdf,      foo'

So the results would now vary

>>> re.split(r'[;,\s]*', line)
['asdf', 'fjdk', 'afed', 'fjek', 'asdf', 'foo']
>>> re.split(r'[;,\s]\s*', line)
['asdf', 'fjdk', '', 'afed', 'fjek', 'asdf', 'foo']

Now, what is the regex you want depends on what is your input you would work on and what is the desired output for all the acceptable test cases.

answered May 29, 2014 at 4:16

Abhijit

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1 Comment

ihightower Over a year ago

thank u for ur input.. excellent example for using the book's regex.

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