Passing data around can easily become confusing. Dataclasses are a fantastic way of structuring and documenting our data and we should be using them a lot more. They are the only standard keyword-based data structure which can serve both our immutable and our mutable data needs. Maybe we should stop teaching collections.namedtuple and typing.NamedTuple and focus on making dataclasses.dataclasses as idiomatic, familiar, and readable as possible. It would be good to have One Obvious Way of creating keyword data structures.

Lambdas are a Python language feature we should provide clear guidance on. Used well they simplify code and are perfectly readable; used poorly, and code becames opaque and bug-prone. Although use should be restrained, an accommodation should be made for Pandas and sorting, albeit with caveats to ensure usage doesn't compromise readability. And a => syntax could be nice.

The Walrus operator risks encouraging buggy code by conflating assignment with evaluation. PHP stands as a warning as to where this can lead. There are few cases where the convenience of the Walrus operator outweigh its risks and even these are not clear-cut. From a When of Python view, the Walrus operator should be in Deprecated Python, or possibly Situational Python but with very few situations accepted. The Walrus will only very occasionally belong in production code.

The for else construct is arguably too confusing for most Python coders and there are simple alternatives that are safe and versatile. A clear candidate for deprecation.

Python pickle is something many of us have had a love-hate relationship with. We've loved it before using it and hated it afterwards ;-) Maybe we should put pickle in the Deprecate Python category?

Python is used by very different groups of people and how we decide which features are Common Python and which are Situational Python must take that into account. If something is common to one group only e.g. data scientists, or enterpise web application developers, it should be considered Situational Python - even if the use case is very common for that group.

Python prides itself on having one obvious way to do things but it is more of an ideal than a reality sometimes. But we should still aim in that direction.

The When of Python is a fledgling community initiative. The goal is to effectively shrink Python so it fits our brains by providing guidance on when we should use particular language features (and when we should not).