Are you aware of PEP 472 https://www.python.org/dev/peps/pep-0472 ? Maybe
you have something different in mind, but for me your idea looks pretty the
same. While the PEP 472 is in Rejected, Abandoned section, I do not
remember any serious criticism of this idea. It’s just that the authors of
that proposal lost interest and it did not receive further progress. And in
this regard, over time, it was abandoned.
with kind regards,
-gdg
пт, 4 окт. 2019 г. в 23:01, Caleb Donovick <donov...@cs.stanford.edu>:
> 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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