Comment by fantod | Hacker News Reader

Comment by fantod | Hacker News Reader

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Exactly. When I initially started using typed Python, I would write code as though I were using a statically-typed language. In order to appease mypy, I found myself increasingly needing to either rewrite my code in awkward ways or add explicit ignore comments.

What happened is I started losing out on the advantages that Python provides as a dynamically-typed language without truly gaining those of statically-typed ones. Then I realized, type hints are just that: hints. They're a form of documentation. In some cases, they're very helpful, but in other cases, it doesn't really make sense to use them. I don't need to appease mypy. The type hints are their for the benefit of myself and other developers.

There is definitely truth to this statement. However often when I write something that’s hard to type, it’s a code smell. Ex. A complex nested map should probably be represented by a few concrete classes/abstractions.

(Similar to when you something you wrote is hard to test, it’s probably just poorly abstracted code.)

I agree and I think a good thing about the type hints is they help uncover these kinds of code smells. But there are definitely cases where it's definitely not worth the effort to fight mypy.

One example is that variable re-assignment can cause type errors in mypy but re-assigning a variable to a value of a different type is an extremely common and reasonable thing to do in Python. Another situation where strict typing can be borderline hopeless is when parsing e.g. very dynamic content like json. Sure you could encode every possible situation using types but this would basically defeat the purpose of using Python for such a task.

> rewrite my code in awkward ways or add explicit ignore comments.

Probably just used to writing poor quality (immediately unintelligible to someone other than the author but functional) code then.

Using typing in Python is a code smell. Lack of understanding of what the language is for and how to use it.

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