在Python中使用多个正则表达式或更大的正则表达式替换

Question

I've switched to Python pretty recently and I'm interested to clean up a very big number of web pages (around 12k) (but can be considered just as easily text files) by removing some particular tags or some other string patterns. For this I'm using the re.sub(..) function in Python.

My question is if it's better (from the efficiency point of view) to create one big regular expression that matches more of my patterns or call the function several times with smaller and simpler regular expressions.

To exemplify, is it better to use something like

 re.sub(r"<[^<>]*>", content)
 re.sub(r"some_other_pattern", content)

or

 re.sub(r"<[^<>]*>|some_other_pattern",content)

Of course, for the sake of exemplifying the previous patterns are really simple and I haven't compiled them here, but in my real-life scenario I will.

LE: The question is not related to the HTML nature of the files, but to the behavior of Python when dealing with multiple regex patterns.

Thanks!

Answer 1

Keep it simple.

I would say that you are safer using smaller Regexes to parse through this stuff. At least that way if it behaves abnormally, you don't have to go digging to find which particular section of the massive Regex is behaving strangely. Providing you have good logging of the replacements you do, it would be trivial to determine the source of the problem, should one arise.

You don't want to run into this

Answer 2

Speaking generally, "sequential" and "parallel" application is not the same and might produce different results, because sequential replacements can affect each other.

As to performance I guess one expression will perform better, but that's just a guess. I personally prefer to keep then complex and use "verbose" mode for readability sake.

Answer 3

I understand your additional comment regarding "its the non-HTML parts I'm cleaning up". Because of the possibility of a latter RE finding and replacing content that a earlier RE replaced, you'd be better off using the "alternative" operator and using a single RE.

Also, consider using BeautifulSoup to load and examine your HTML files. This will assist in finding the appropriate parts of your text with far less risk of capturing some HTML construct when you were just intending on on replacing some text.