On Thu, Dec 19, 2019 at 6:36 PM Eli the Bearded <*@eli.users.panix.com> wrote: > > I recently saw a link to an old post on a blog and then started looking > at the newer posts. This one: > > https://leancrew.com/all-this/2019/11/the-key-to-sorting-in-python/ > > discusses ways to deal with useful sorting of movie / television show > titles. Some initial words should be re-ordered for sorting purposes > (_Adventures of Huckleberry Finn, The_), roman numbers should sort like > regular numbers (_Rocky V_ comes before _Rocky IX_), and something needs > to be done about sorting accented vowels. > > But what caught my eye most, as someone relatively new to Python but > with long experience in C in Perl, is sorting doesn't take a > *comparison* function, it takes a *key generator* function, and that > function is supposed to transform the thing into something that the > native comparison knows how to compare. > > This seems a strange choice, and I'm wondering if someone can explain > the benefits of doing it that way to me. >
If you provide a comparison function, it has to be called for every pair that need to be compared. Plus, it usually has to be written such that it does the same thing twice: arrayInJavaScript.sort((x, y) => x.some_attr[0] > y.some_attr[0]) python_list.sort(key=lambda x: x.some_attr[0]) Thirdly, a key function can easily handle three-way comparisons, whereas a comparison function usually just offers two-way - it's harder to write a comparison function for -1, 0, 1 returns. So the sort is much less likely to be stable. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
