> The desired type is known; it's "Addable" (i.e., "doesn't throw an exception when the built-in add operator is used").
The mistake both you and the reddit posts' author make is treating the `+` operator the same as you would an interface method. Despite Python having __add__/__radd__ methods, this isn't true, nor is it true in many other programming languages. For example, Go doesn't have a way to express "can use the + operator" at all, and "can use comparison operators" is defined as an explicit union between built-in types.[0] In C# you could only do this as of .NET 7, which was released in Nov 2022[1] -- was the C# type system unusable for the 17 years prior, when it didn't support this scenario?
If this were any operation on `a` and `b` other than a built-in operator, such as `a.foo(b)`, it would be trivial to define a Protocol (which the author does in Step 4) and have everything work as expected. It's only because of misunderstanding of basic Python that the author continues to struggle for another 1000 words before concluding that type checking is bad. It's an extremely cherry-picked and unrealistic scenario either from someone who is clueless, or knows what they're doing and is intentionally being malicious in order to engagement bait.[2]
This isn't to say Python (or Go, or C#) has the best type system, and it certainly lacks compared to Rust which is a very valid complaint, but "I can't express 'type which supports the '+' operator'" is an insanely esoteric and unusual case, unsupported in many languages, that it's disingenuous to use it as an excuse for why people shouldn't bother with type hinting at all.
[0] https://pkg.go.dev/cmp#Ordered
[1] https://learn.microsoft.com/en-us/dotnet/standard/generics/m...
[2] actually reading through the reddit comments, the author specifically says they were engagement baiting so... I guess they had enough Python knowledge to trick people into thinking type hinting was bad, fair enough!