I've seen the same in Python, probably a dozen times. Sometimes folks think it's ugly (un-pythonic) but there's plenty of cases in the standard library to point to.
That's because the Python regex module caches the regexes it compiles, so it only happens once. It's proper and good usage to specify the regex string inline, even in a hot path.
I'd only use a variable when I'm using the same regex multiple times in code, and even then I could still just have the variable be the string.
> That's because the Python regex module caches the regexes it compiles, so it only happens once. It's proper and good usage to specify the regex string inline, even in a hot path.
Last time I had a look the regex cache was pretty small (few hundred entries) and gets completely cleared when full. Might have improved since, but historically it was very simplistic.
I disagree that it’s “proper and good usage” to specify regex inline. It’s fine for many usages but that’s as far as I’d go.
Gotta agree with the sibling comments here. The performance difference is definitely smaller than it used to be, but there's still good reasons to keep compiled regexes in a module scope.
Caveat: I write libraries, not "production" code; my requirements are significantly more strict. One thing I can't do is make assumptions about where my code will run. If you're using my library, and you compile a whole bunch of regexes, they'll evict my regexes from the cache. I don't want the performance of my library to suffer, so I'll keep them in the module scope.
