> On 7 Oct 2019, at 16:36, Batuhan Taskaya <isidenti...@gmail.com> wrote:
>
>
> In fact, that would be a cool feature for ORMs. IMHO instead of ugly call
> chain with filters, slicing is a better option (on `__class_getattr__`). As
> said there are some disadvantages but i think this proposal deserves a PEP.
I really don't see why. Is () so much different than [] to you? Because that
seems like the only difference here.
>
>> On Fri, Oct 4, 2019, 10:59 PM Caleb Donovick <donov...@cs.stanford.edu>
>> wrote:
>> While there is no restriction on passing dicts to getitem. Doing so tends
>> to be a bit ugly. I have two main use cases in mind for this syntax.
>>
>> The first and perhaps the most obvious, is doing relational queries.
>> ```
>> where_x_1 = db[x=1]
>> ```
>> is more beautiful than
>> ```
>> where_x_1 = db[dict(x=1)]
>> where_x_1 = db[{'x': 1}]
>> # or by abusing slices
>> where_x_1 = db['x':1]
>> # or in the style of Pandas
>> where_x_1 = db[db['x'] == 1]
>> ```
>>
>> Beyond relational queries my own personal use case is a shorthand for
>> dataclasses / protocols.
>> ```
>> foo: ProtoRecord[x=int, y=int] = DataRecord[x=int, y=int](0, 1)
>> ```
>> where `DataRecord[field0=T0, ..., fieldk=Tk]` generates
>> ```
>> @dataclass
>> class Record:
>> field0: T0
>> ...
>> fieldk: Tk
>> ```
>> and `ProtoRecord[field0=T0, ..., fieldk=Tk]` generates a similar protocol.
>>
>> Allowing key value pairs in geitem need not change the interface of getitem.
>> All the key value pairs could be collected as a dict and passed to getitem
>> as the index. Similar to how the all the positional arguments are gather
>> into a single tuple.
>> ```
>> class Foo:
>> def __getitem__(self, idx):
>> print(idx)
>>
>> f = Foo()
>> f[x=1, y=2] # {'x': 1, 'y': 2}
>> ```
>> This would make any legacy code using normal dicts as keys (I don't know how
>> prevalent that is) automatically work with the new syntax.
>>
>> There doesn't necessarily need to be support for mixing of tuple based
>> indexing and keyword indexing. i.e.
>> ```
>> obj[0, x=1] # SyntaxError
>> ```
>>
>> I don't really know anything about parsers but I think the grammar could be
>> extended without issue with the following rule:
>> ```
>> subscriptlist: ... | kwargsubscript (',' kwargsubscript )* [',']
>> kwargsubscript: NAME '=' test
>> ```
>> if `NAME '=' test` would result in ambiguity similar to argument it could be
>> `test '=' test` with a block in ast.c
>>
>>
>> - Caleb Donovick
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