[rbehrends]

As somebody who uses and likes both Kotlin and Python (and quite a few other languages), I'd be cautious with using a subjective term such as "more expressive", too, but I can possibly shed some light on where such feelings come from.

Personally, I see Kotlin as the closest thing to a statically typed Smalltalk that we have among major languages, and that's a major draw.

A key part here is that Kotlin closures are fully-featured equivalents of Smalltalk blocks (up to and including even non-local returns [1]), whereas in many other languages that falls short. Java does not allow mutation of local variables and Python restricts lambdas to normal expressions.

I find code whose behavior can be parameterized by code to be an essential feature of modern-day programming and this should be as frictionless as possible.

This is also a situation where syntax matters, and while it isn't quite as nice as Smalltalk, Kotlin's syntax (esp. with trailing closures) make such code as readable as possible in a brace-style language with minimal additional syntactic noise.

In a similar vein, the functionality of Smalltalk's cascades is offered through scope functions [2], especially `.run {}`.

But ultimately, fully-featured closures (and the fact that they are widely used in the standard library) power a lot of the things that people seem to like about Kotlin.

That does not mean that there aren't downsides. The limitations of running on the JVM are one (e.g. while Kotlin has workarounds for the JVM's type erasure, they're still workarounds), and then Gradle is arguably Kotlin's weakest point (which apparently even JetBrains are seeing, given their investment in Amper).

That said, personally I'd say Kotlin's static typing and performance would be the primary reasons for me to reach for Kotlin over Python, not necessarily expressiveness. Type annotations in Python + mypy etc. just aren't the same experience, and writing performance-sensitive code in Python can be very tricky/hacky when you can't delegate the hot paths to numpy or other existing C/C++/Rust libraries.

Conversely, Python often has a leg up when it comes to fast prototyping and scripting, even with Kotlin Worksheets in IntelliJ IDEA and with kscript.

[1] Which, to be clear, are a nice-to-have thing, not essential, but still impressive that even that was covered, when previously Ruby was the only major language I know of that did it.

[2] https://kotlinlang.org/docs/scope-functions.html