Is there a way to parse regex from right to left in python?
I have a few huge regexes that take about a second to run on my input, for a total run-time of a few minutes. So I tried to test the performance of my regexes, and regexhero had an option to parse regex from right to left, which resulted in about a million times faster execution because of quicker failing.
Yes, the way is to reverse the string (and to write the pattern according to the new string):
string:
'John likes to eat mushrooms'[::-1]
pattern (what like John?):
r'^(.+) sekil nohJ$'
You can also change the re module to the regex module that provides a reverse search flag (?r):
>>> import regex
>>> regex.findall(r'(?r)\w+(?=\W+\w*e)', 'John likes to eat mushrooms')
['to', 'John']
(Take care of this feature, as .net RightToLeft option, results may be counter-intuitive.)
