D solved the problem with what happens with (a == b == c) in an unusual way. It gives an error message. Both the C way and the Python way are considered wrong. You're going to have to add ( ) to clarify.
Rust also gives a custom error message [0] that explicitly explains that "comparison operators cannot be chained" and shows you how to rewrite the expression using `&&`.
Which makes me wonder whether they came up with this idea themselves or if they borrowed it from D.
In any case, I think that this is the only reasonable solution for new languages. Because if you go with C way it will be surprising for people who expect Python way and vice versa. So, making this syntax illegal is the only way to uphold the principle of least astonishment [1].
I gave several presentations that included this back in the 2010-2012 timeframe, and it had already been in the language for maybe a decade.
When I implemented it, I had seen many knock-down drag-out debates about which was the best way to deal with it, and none of them mentioned simply making it illegal.
It was another one of those features that were based on my experience designing aircraft systems.
Another one adopted by pretty much all languages since D is the _ in numeric literals (although C++ used a backtick). It was just something that was obviously right once you saw it. But I didn't originate it, I cribbed it from Ada. I've always had a soft spot for Ada.
