[all languages]
You could note that this kind of a construction is called a closure.

It would make it easier for beginners to find and learn about this.

Depends on the language you are using...

It's too hot (t, double o) in the description.

This is a minor thing, but no reason not to correct this :)

You know what, that's actually a good point. In some cases you can be reasonably confident that the method you're writing will only concatenate a small number of strings or will not be run a huge number of times, so the difference in performance is going to be insignificant.

I should probably have phrased my initial response differently, along the lines of "yo, concatenating is ok in small doses, but .join() is a lot faster if you are gonna do that with a lot of strings; it also makes you look good on job interviews". Unfortunately, don't think I can edit it.

Cheers :)

Unfortunately this is NOT a 'best practice'. String concatenation using + operator is some 30 times slower than using "separator".join(iterator_to_be_joined).

For additional reading: https://waymoot.org/home/python_string/