[Python-ideas] Possible method of distinguishing between set-literals, dict-literals, and odict-literals

Carl Johnson cmjohnson.mailinglist at gmail.com
Tue Jun 16 23:29:41 CEST 2009

Ron Adam wrote:
> Ben Finney wrote:
>> Carl Johnson writes:
>>> we could introduce an empty set-literal and an odict-literal, and add
>>> a more explicit form to replace the existing set literal.
>> What do you mean by “more explicit”? The existing set literal syntax
>> is quite explicit.
> I think Carl is thinking that it is more concise and easier to read.

Yes, that's part of it. Thank you. What I mean by "explicit" in this
case is something like "harder to accidentally misparse in your mind."
So for example if you see {f(i) for i in my_data} obviously it is
unambiguously a set-comprehension, but if you aren't paying close
enough attention you might mistakenly think it was a
dict-comprehension. On the other hand, s{f(i) for i in my_data} more
or less screams, "I am a set-comprehension!" On the other hand, it's
ugly, and the BDFL doesn't like it. So, it's probably a dead idea now…

Terry Reedy wrote:
> Literals represent constants. They are sensibly interpreted into constants
> sometime before runtime, even if at a later stage than I thought.

I'm not sure what you're getting at here. What about d = {} ? That's
not immutable. Nor is l = [1, 2, 3]. Or by "constant" do you just mean
something that will be the same at the *start* of every program, but
it may or may not change before the program is over?

- - - -

I think ["a": 1, "b": 2] is an interesting syntax, and certainly more
elegant than o{"a": 1, "b": 2} but I worry that it could be ambiguous.
I can't think of any way to do it off the top of my head, but might
there be some valid way of writing l[1:2] that could be ambiguous
between the two? If nothing else, it would confuse newbies about what
[:] means: slice or odict?

-- Carl

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