Are you aware of PEP 472 https://www.python.org/dev/peps/pep-0472 ?

That is indeed the same idea, though perhaps the details are a bit different.

This example from the PEP:

gridValues[x=3, y=5, z=8]
Makes me wonder: 

Should that yield the same results as:

gridValues[3,5,8]
Much like positional and keyword arguments work on function calls?

I suppose that would be up to the implementation, as __getitem__ doesn’t currently provide much help with parsing out what’s in there, other than making slice objects.

But if something like this did go forward, it would be nice to provide utilities, maybe built in, that would parse and sort out the “arguments”, similar to function calls.

-CHB


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 <donovick@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
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-leave@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/EUGDRTRFIY36K4RM3QRR52CKCI7MIR2M/
Code of Conduct: http://python.org/psf/codeofconduct/
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-leave@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/XPQC6AIX2REI5W6EKCRRI7UEGJWVEOC6/
Code of Conduct: http://python.org/psf/codeofconduct/
--
Christopher Barker, PhD

Python Language Consulting
  - Teaching
  - Scientific Software Development
  - Desktop GUI and Web Development
  - wxPython, numpy, scipy, Cython