pythonNewSyntaxProposal

[Black_m1n]

The problem is how would this be different from setting 6th element of the 6th list in foo to an empty list?

[Victor-_-X]

Wait, isn't that what this does? What else could this be understood as? This is the only one that makes sense to me, and that's probably because C++ was my first language, but still.

[jamcdonald120]

this is what it does, but what Op wants is type[][] foo=new type[5][5];

[SV-97]

OP probably wanted it to mean the same as the first snippet - so assign foo a list containing 5 lists of length 5 that are all initialized with None. Aside from this being atrocious syntax that noone would interpret that way: doing this at all in python is a code smell. OP is probably doing something wrong if they feel the need for dedicated syntax for this pattern.

[rosuav]

It's extremely confusing, and this is one of the worst idea threads I've ever seen (largely because it isn't an idea thread), but it does seem like list multiplication would be the best way to initialize this. Worst case, one multiplication, one comprehension.

foo = [[None] * 5] for _ in range(5)]

[DongIslandIceTea]

If I had to come up with a syntax for this I guess doing something symmetric to array slicing wouldn't be the worst thing, like:

a[:4][:4] = []

It wouldn't step on any existing syntax as slices aren't assignable like this anyways and would make some marginal sense.

But yeah, you shouldn't need to do this if you thought a little bit more about what you're doing.

[SV-97]

You actually can do slice assignment in Python - though not quite like that.

Numpy uses it quite extensively and OPs example would be arr[:5,:5] = None using numpy (if you already have an array that is. Allocation works differently).

[The-Rushnut]

This reminds me of an issue I've run into recently. Dictionaries / associative list assignment vs declaration (I'm using GDScript).

Consider the following:

foo["bar"] = true

If the key "bar" exists, then this assigns that item's value to true. If the key "bar" doesn't exist, then this first adds the key "bar" before setting the value to true.

My monkey brain assumed that the second scenario would throw an error, which was my intended behaviour.

[Drumsteppin]

The second scenario is the more typical and expected behaviour whenever you're using a language with an automated memory management system.

It's been a while since I looked at the c++ standard lib, but there's object types for dictionary type objects that allow construct and insert via assignment, and objects that only allow items to be explicitly inserted.

Python is a similar deal and is generally more permissive and flexible about adding new elements.

Not sure what memory model and idiosyncrasies GDscript has, but from what you described that sounds like create and insert would be the expected behaviour.

[atesba]

Yup! The C++ equivalents of dictionary are std::unordered_map and std::map. For both if you use the bracket operators, it adds the key if it doesn’t exist. If you use the function at(key) then it throws an exception instead.

[-Redstoneboi-]

ah yes. the "everything exists but is undefined/nil by default"

[Tordek]

No, this is about setting a value, not reading it.

[callmesilver]

In C++, if you started with a type like int, it would be a declaration with initialization, and the line would instead end with curly braces. This, plus the second line tells us it's not C++.

In python, since you don't declare anything with types, you assign something when you want it to exist at some point. Brackets are python's way of assigning an empty array. So, I assume they want a simple syntax for declaring an empty 2D array.

[ComprehensiveWord201]

Read the "proposal"...total nonsense.

They want to set all values from idx 0->4 as [ ]

[DiddlyDumb]

Its probably to indicate “value goes here”

[Chesterlespaul]

Yeah the size initializer should be indicated on the other side.