Comment by leephillips | Hacker News Reader

Comment by leephillips | Hacker News Reader

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It’s hard to remember what order to put things in, because the two methods follow opposite conventions. And that’s because this type of OO design has no obvious method of organization.

In the first case, I want to do something to a list: join it into a string. So, clearly, I need a list method? But no, I need to engage in some form of indirection; for some reason, I need to reach for a string method. Even if there is no string that I want to use as a delimiter. In that case, I need to use a string method on an empty string.

OK, I’ll play along. Now I want to take the string and split it into an array. Now that I’ve been educated, I know better than to try the sensible thing. Pre-enlightenment, I would have reached for a method applied to the thing that I wanted to transform. But now I know I should think backwards, and use a method applied to the delimiter. OOPs.

Here it is in Julia:

     julia> join([1 2 3], ", ")
     "1, 2, 3"


     julia> split("1, 2, 3", ", ")
     3-element Vector{SubString{String}}:
      "1"
      "2"
      "3"

Note how they are both functions. The data that they operate on is the first argument, in both cases. The optional second argument is the obvious next most important thing, the delimiter. Other optional arguments come after that. There is nothing to remember, because it makes sense.

The Python FAQ itself adresses this: https://docs.python.org/3/faq/design.html#why-is-join-a-stri...

You'll have to decide if you find that convincing. I understand your point and kind of wish I hadn't read this thread because I'm more torn than before.

Not convincing exactly, but I’m glad to know the thinking behind it, thank you. How are you torn?

That’s fair Lee. I think I’d accidentally stumbled upon the logic for .join acting on the separator rather than the iterable, but I do agree it’s awkward unless you’re trying to figure out why it is (which is poor design), and certainly not how most people think, especially with the inconsistency of split not acting on the separator.

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