On Mon, Mar 25, 2019 at 12:28 AM Jonathan Fine <jfine2...@gmail.com> wrote: > > Disclaimer: I've not recently read any discussions of this topic. And > everything I say is my own opinion. > > SUMMARY > The syntax of Python's string join operator are a consequence of Python's > core design decisions and coding principles, together with the semantics of > join. I'll explain this in a series of posts. > > Why str.join? Wouldn't list.join be better? > =============================== > Python variables don't have types. Python objects do have types. When writing > Python, don't test for the type of an object, unless you have to. Instead, > test to see if the object has the methods you need. > > Eg help(dict.update) > update(...) > D.update([E, ]**F) -> None. Update D from dict/iterable E and F. > If E is present and has a .keys() method, then does: for k in E: D[k] = > E[k] > If E is present and lacks a .keys() method, then does: for k, v in E: > D[k] = v > In either case, this is followed by: for k in F: D[k] = F[k] > > Now for the semantics of string join. By Python principles > From a str and an iterable > The string join operator > Produces a str > > You question amounts to this. Should the signature be > (str, iterable) -> str # Informal type signature of join. > or should it be > (iterable, str) -> str > > At first glance, there's no way of choosing. But in Python we prefer > aaa.join(bbb) > to > from somewhere import join > join(aaa, bbb) > > So the question now becomes: Choose between > str.join(iterable) > iterable.join(str) > > There is some sense in having list.join. But in Python, we can't join the > elements of a list without getting an iterable from the list (unless there's > something like very special short-cut-semantics built into Python). > > So in Python the choice is between > str.join(iterable) > iterable.join(str) > > Now str.join looks more attractive. But I said, without thinking ahead, that > the syntax of Python's string join operator is a consequence of Python's core > design decisions and coding principles, together with the semantics of join. > > I'm not quite there yet, there's a gap to fill. I'll pause for a day or two > now, just in case someone else wants to JOIN in the discussion, and perhaps > fill the gap. >
It's way WAY simpler than all this. "Iterable" isn't a type, it's a protocol; in fact, "iterable" just means "has an __iter__ method". Adding a method to iterables means adding that method to every single object that wants to be iterable, but adding a method to strings just means adding it to the str type. And, this is a topic for python-list, not python-ideas, unless someone is proposing a change. ChrisA _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
