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One thing that drives me nuts is that enthusiasts of python type hints claim that it means you will no longer give a function the wrong type of value and thus e

One thing that drives me nuts is that enthusiasts of python type hints claim that it means you will no longer give a function the wrong type of value and thus eliminate a class of errors. This should imply that you no longer need to test for those types of problems. Since writing tests is not free, and often not even trivial, this would be a huge benefit of type hints. But, because type hints are just window dressing in Python, you still have to write those tests. So now when you make a change, you not only have to update your tests but also update your type hints everywhere. As far as I can tell, type hints just double the work for little to no benefit. If they actually removed a need for unit testing, that would be a different story, but then it wouldn't be Python anymore. If I want to use types to enforce things, I'd prefer to use a language designed for that. But I choose Python because it lets me get things done quickly. Despite helping you out in some cases, overall maintaining type hints are a drag on that feeling of getting things done quickly. The last thing I want to do when writing Python is spend an afternoon composing a complicated TypeVar arrangement to express the full range of inputs my function can handle. What this article talks about (Protocol) seems to be at least an improvement in that regard, as you can worry about what your function does instead of what your types do.

dragonwriter 5y ago
> But, because type hints are just window dressing in Python, Type annotations are not window dressing in a Python workflow using typechecking tools over the final code base, unless you explicitly tell the typechecker to ignore a detected error. It's true that a type annotated library can't necessarily rely on downstream clients to have type discipline, and some library packages may not be fully annotated, which may create gaps to address. > If I want to use types to enforce things, I'd prefer to use a language designed for that. Python's type annotations were designed largely to make Python compatible with a separate existing language designed for that purpose; there's a reason mypy’s domain is mypy-lang.org > What this article talks about (Protocol) seems to be at least an improvement in that regard, as you can worry about what your function does instead of what your types do. Protocols are types; specifically, they are structural types.
- DerArzt 5y ago
  To add to this, when we are reading/writing python source code there are types involved. The question becomes do we want the types to exist only in our heads or also denoted in the source. To me even though the type annotations don't provide the same kind of guarantees that the type system of say Haskell does, they do increase the readability of the source code. Finally (and this is more of my workflow), I utilize a build tool that has a mypy --strict call that will check my type annotations and alert me when things don't match up.

dragonwriter 5y ago

> But, because type hints are just window dressing in Python, Type annotations are not window dressing in a Python workflow using typechecking tools over the final code base, unless you explicitly tell the typechecker to ignore a detected error. It's true that a type annotated library can't necessarily rely on downstream clients to have type discipline, and some library packages may not be fully annotated, which may create gaps to address. > If I want to use types to enforce things, I'd prefer to use a language designed for that. Python's type annotations were designed largely to make Python compatible with a separate existing language designed for that purpose; there's a reason mypy’s domain is mypy-lang.org > What this article talks about (Protocol) seems to be at least an improvement in that regard, as you can worry about what your function does instead of what your types do. Protocols are types; specifically, they are structural types.

DerArzt 5y ago
To add to this, when we are reading/writing python source code there are types involved. The question becomes do we want the types to exist only in our heads or also denoted in the source. To me even though the type annotations don't provide the same kind of guarantees that the type system of say Haskell does, they do increase the readability of the source code. Finally (and this is more of my workflow), I utilize a build tool that has a mypy --strict call that will check my type annotations and alert me when things don't match up.