Hi Stefano,
Thank you for submitting PEP 637 (Support for indexing with keyword
arguments). The Steering Council has reviewed the PEP and after careful
consideration, we have decided to reject the PEP. There are a number of
reasons for this, but fundamentally we do not believe the benefit is great
enough to outweigh the cost of the new syntax.
The benefits of the new syntax as outlined in the PEP are not particularly
strong, and community support for the new syntax seems low. The new syntax
doesn’t provide an obvious way to do something that is currently
error-prone, and doesn’t open up new possibilities that were not possible
before. While there are certainly cases that could use the new syntax, for
many of them it’s not clear that it would be a win, or that third-party
libraries would indeed use the syntax. The Steering Council isn’t really
convinced by any of the suggested uses in the PEP.
The strongest argument for the new syntax comes from the typing side of
Python. The Steering Council is not particularly convinced it is of
significant benefit to the static type checking language, but even if it
were, at this point we’re reluctant to add general Python syntax that only
(or mostly) benefits the static typing language. If the syntax would be of
great benefit to static typing, it might be time to discuss letting go of
the requirement that the typing language be a subset of Python -- but
whether this feature is important enough to consider that is up to the
typing community.
The SC considers the cost of the new syntax significant. It’s not a natural
fit, as shown by the corner cases discussed in the PEP. It’s difficult to
teach, as indexing and function calls are not as interchangeable or
equivalent as they may appear. Looking at more complex expressions with the
new syntax, mentally parsing them is significantly harder than the
equivalent without the new syntax, even if it requires more lines of code
to do the same thing.
In addition to all that, the SC is worried about the performance of
indexing in CPython and in other Python implementations, considering it’s a
very common operation, and about the suggested new __getitem__ protocol,
particularly the confusing corner cases of indexing with keywords and zero
or one positional items. These are not, however, the main reason we decided
to reject the PEP.
With our appreciation,
For the whole Python Steering Council,
Thomas.
--
Thomas Wouters