[Python-3000] Set literals - another try (original) (raw)

Josiah Carlson jcarlson at uci.edu
Tue Aug 8 19:36:40 CEST 2006

Talin <talin at acm.org> wrote:

Part 1: The concrete proposal part. I noticed that a lot of folks seemed to like the idea of making the empty set resemble the greek letter Phi, using a combination of parentheses and the vertical bar or forward slash character. So lets expand on this: slice Phi in half and say that (| and |) are delimiters for a set literal, as follows: (|) # Empty set (|a|) # Set with 1 item (|a,b|) # Set with 2 items The advantage of this proposal is that it maintains visual consistency between the 0, 1, and N element cases.

That's quite a bit of punctuation to define a set literal. In fact, for 1+ element sets, it's only 1 character shy of the set() punctuation, while also being more difficult to type on at least US keyboards.

And if I remember my set math correctly, phi wasn't the character generally used, it was usually a zero with a diagonal cross through it, making (/) a better empty set literal. But from there, the notation devolves into a place I don't want to go.

Part 2: The idle speculation part, not to be considered as a actual proposal.

I've often said that "whenever a programmer has the urge to invent a new programming language, that they should lie down on the couch until the feeling passes".

Presumably you again don't remember the source of this quote, but it is still applicable.

As a thought experiment, I decided to apply this idea to the Python set literal case - i.e. if we were going to do a massive "do over" of Python, how would we approach the problem of set literals?

The syntax that comes to mind is something like this: a = b|c

The pipe character/bitwise or operator doesn't say to me "make a set".

Knowing what I do about set math, the only literal that really makes sense to me is: {a,b,c,...}

With the empty set being: {/}

Interstingly enough, the non-empty set case has already been proposed, and if I remember correctly, was generally liked, except for the somewhat ambiguity with regards to dictionary literals.

I personally don't see much of a use for set literals, considering that there is a non-ambiguous spelling of it currently; set(...), whose only cost above and beyond that of a set literal is a global name lookup. It is 'different' from some other first-class objects (tuple, list, dictionary, string, unicode, ...), but other first-class objects also require such spelling: bool, enumerate, iter, len, property, reduce. Each of which may be used sufficiently often to make sense as having a syntax for their operations, though perhaps only len having an obvious syntax of |obj| -> len(obj), though |obj| could also mean abs(obj), but presumably objects would only ever have len or abs and not both. I digress.

-.5 for a set literal syntax at all, -1 for offering your particular set literal variant, -2 for your change propagating to dictionaries and beyond.

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