程式扎記: [ Python 常見問題 ] Matching any character including newlines in a Python re

2019年4月3日星期三

[ Python 常見問題 ] Matching any character including newlines in a Python re

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Question
I want to use re.MULTILINE but NOT re.DOTALL, so that I can have a regex that includes both an "any character" wildcard and the normal . wildcard that doesn't match newlines.

Is there a way to do this? What should I use to match any character in those instances that I want to include newlines?

How-To
To match a newline, or "any symbol" without re.S/re.DOTALL, you may use any of the following:

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[\s\S]  
[\w\W]  
[\d\D]  

The main idea is that the opposite shorthand classes inside a character class match any symbol there is in the input string.

Comparing it to (.|\s) and other variations with alternation, the character class solution is much more efficient as it involves much less backtracking (when used with a * or + quantifier). Compare the small example: it takes (?:.|\n)+ 45 steps to complete, and it takes [\s\S]+ just 2 steps.

Let's test this solution a little bit:

>>> import re
>>> astr = '<html></html>'
>>> re.sub('', '', astr) # Won't work in multiple line
'<html></html>'
>>> re.sub('', '', '<html></html>') # Only work in single lin
'<html≷</html≷'

>>> re.sub('', '', astr) # Work for both single/multiple lines
'<html>&t;/html>'
>>> re.sub('', '', '<html></html>')
'<html></html>'

Supplement
* String services : re — Regular expression operations

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[ Python 常見問題 ] Matching any character including newlines in a Python re

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2019年4月3日 星期三

[ Python 常見問題 ] Matching any character including newlines in a Python re

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[Git 常見問題] error: The following untracked working tree files would be overwritten by merge

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2019年4月3日星期三