Adding Empty Set Literals to Python

http://philipbjorge.com/2013/03/16/adding-empty-set-literals-to-python/

by philipbjorge • 13 years ago

41 46 13 years ago

Maybe Guido doesn't like it because it looks weird when compared to the rest of Python's syntax? Still, I think it's cool. Having sets availably without importing anything is one of the things I love about Python.

set = <> is still available.

rdtsc• 13 years ago

you don't import sets , set() is available right away.

jmmcd2• 13 years ago

set = <> is still available

Did this get misformatted? I don't know what you mean.

uraza2• 13 years ago

I believe sciencerobot is saying that "<>" could be used as the empty set literal.

sciencerobot2• 13 years ago

Yes, that was the idea. I don't think it would be confusing to the parser.

uraza2• 13 years ago

set = <> looks like the other empty container literals, but it's not consistent with the literal notation for sets with one or more elements: my_set = {1,2,3}.

sambe• 13 years ago

What about supporting <1, 2, 3> as well, and eventually deprecating the existing way? The end result would be much nicer.

SilasX• 13 years ago

Is it just me, or is it a little ... obsessive to be this annoyed with having to use `set()` instead of `{@}`?

npc• 13 years ago

What, you've never gone and hacked an interpreter because you were mildly annoyed by something? I don't think he actually means for it to be used in production.

johnsoft• 13 years ago

I vaguely recall seeing a mailing list thread where `{-}` was proposed. I think it was rejected based on parsing ambiguity, i.e. `{-1}` vs `{-}`. (Or it's possible I might be losing my memory)

philipbjorge4• 13 years ago

I originally implemented it that way and had that exact same issue (it's one of the revisions on github). Similarly, {/} would also be a problem.

digisign2• 13 years ago

How about {,} or s{} ?

yen223• 13 years ago

Wouldn't it lead to the same problem of a lack of consistency?

    dict: {} 
    list: []
    tuple: ()
    set: {-}

tantalor2• 13 years ago

    There should be one-- and preferably only one --obvious way to do it.
    Although that way may not be obvious at first unless you're Dutch.

dechols• 13 years ago

Which is more Pythonic?

list() or []

dict() or {}

set() or ????

I would argue that the left is more pythonic and expressive.

tantalor2• 13 years ago

Don't forget tuple() and ().

I don't think any are more pythonic. They are all valid python.

raymondh• 13 years ago

Executive summary: If you don't like part of the language, it is really easy to add your own hack and make it worse ;-)

Really, you should trust the core developers on this one. Empty set literals are missing from Python for a reason.

philipbjorge4• 13 years ago

I just wish someone could find the old discussions...

The main argument I could see against empty set literals was how wrong it felt adding it to the grammar. Even adding 3 lines of code for the feature, felt like it was just creating chaos in a zen-like codebase.

antfarm2• 13 years ago

http://mail.python.org/pipermail/python-3000/2007-April/0066...

http://mail.python.org/pipermail/python-ideas/2008-January/0...

nnq2• 13 years ago

imagine that the "chaos" you are adding to the implementation is actually subtracted from its "interface" and consequently from all code that will be written thereon... sometimes you need to "add complexity"/"destroy order" to create more order at a higher level :)

nnq2• 13 years ago

You're right on trusting the core developers, but "for a reason" type arguments are not the way to do things. I love Python because it's so practical and manages to stop codebases from devolving into overengineered incomprehensible messes, but I hate tons lots of things about it, and more generally I hate its "worse is better" approach (http://www.jwz.org/doc/worse-is-better.html) to many things (because for Guido, if "worse" is "simpler to explain and implement", he always chooses it, always implementation simplicity over nice "interface" features and also over "interface" consistency... I almost want to shoot the man when I read arguments like http://www.artima.com/weblogs/viewpost.jsp?thread=147358 coming from a very smart person like him). OP's complaint is valid imho, consistency is f important, because small inconsistencies pile up and make a language harder to learn (yeah, you don't notice them once they're in your "muscle memory", but "learnability" is important for a language and this is why I like Python and I hope it doesn't lose this quality by slowly accreting inconsistencies). Hopefully his blogpost is a message that reaches Guido and the core developers and nudges them even a little bit towards a better path!

rakha• 13 years ago

"I thought {@} would be a good for an empty set because it arguably looks like the empty set symbol"

I'm just nitpicking but I don't think this is a good justification - If the @ symbol looks like the empty set symbol, then {@} is the set containing the empty set

hwiechers• 13 years ago

I think it would be best if empty dictionary was {:} and empty set was {}. Of course, it would be insane to make this change.

polemic• 13 years ago

That ain't orthogonality, this is orthogonality:

    dict() = {}
    set() = <>
    tuple() = ()
    list() = []

(btw, does anyone actually use `<>` as `!=`?)

Erwin• 13 years ago

They finally got rid of <> in Python 3 (together with the `` as being alias for repr).

masklinn2• 13 years ago

And they're not going to add new syntax to Python 2.7 (and the core team has been empathetic that there would not be a 2.8), so `<>` could easily be repurposed for "empty set".

Of course `<1, 2, 3, 4>` would then have to be an alternative set literal.

derefr• 13 years ago

It seems to me that our real problem here is the dearth of easily-accessible bracket characters on US-standard keyboards:

    x = 【1, 2, 3】
    y = 【】

;)

jrockway2• 13 years ago

I personally prefer dict() to {} anyway, so I don't really miss the lack of an empty set literal.

Adding a set literal was a slippery slope anyway. Where's my frozenset literal? Where's my namedtuple literal?

(I also don't particularly like the {} syntax for dicts, because there is {'too_much': 'quoting'} which I find rather ugly. I much prefer dict(too_much='quoting') or, even better, Perl's solution: { too_much => 'quoting' }.)

mkhattab3• 13 years ago

I also prefer the dict() function as well as JS object literals but it's too bad there's a performance penalty to using dict().

jrockway2• 13 years ago

There's a performance penalty to using Python, too. I wouldn't let miniscule detail affect whether or not you like the code you're reading. (By that logic, you should represent sets as {'element': 1} instead of set('element'), because calling the function "set" is slower than making a dictionary object from the special syntax.)

vbtemp• 13 years ago

> What I learned: It’s not always hard to make interesting changes to large projects.

Should be, it's not always hard to make interesting changes to very well-designed and well-architected projects

codesuela• 13 years ago

The webfont doesn't load for me because I have Ghostery installed (it blocks remote tracking scripts) so the page is all blank except for the code snippets (because Adobe Typekit is blocked). You should consider adding a fallback font.

philipbjorge4• 13 years ago

Thanks and will do!

I just added a 1 second timeout that puts a default font on if the webfont hasn't loaded. Just tested with ghostery and it should be good to go.

Adding Empty Set Literals to Python

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