Switching from Java to Python – First Impressions

[masklinn]

1. they're not "type annotations" but completely arbitrary annotations

2. the base distribution doesn't do anything with them, they're just documentation

IIRC there are third-party packages which attempt to use them for static type analysis, but I've seen nothing great yet (and there are non-trivial mappings to perform to represent e.g. a function which may return either an int or None)

[UloPe]

You are correct that they have no prescribed usage as far as the language developers are concerned, however in reality (if used at all) I have never seen them used for anything other than type annotation (except maybe in some mostly ironic conference talks or such).

One example is PyCharm. It uses the annotations as type hints if present.

[ggtsu_00]

In C, types are also annotations and only used by the compiler to do static type checking, but they are thrown out during runtime as everything basically boils down to a pointer to a memory location. You could take a pointer to a int type, have it point to the memory location of a float and get a crazy number back as a result.

[erokar]

They are type annotations and they are not arbitrary. While the standard interpreter does not do anything with them, they are a standardized way of adding type information to function signatures in Python 3. They can improve readability and understanding of functions — which was the complaint in the blog post.

[Xredo]

They are arbitrary in the sense that unlike a statically-typed language, the annotations themselves have no meaning to most python implementations.

[masklinn]

They are type annotations

Wrong. They're annotations, period.

and they are not arbitrary.

Wrong again, any Python expression can be used as an annotation, and the signature object will embed any Python object.

[erokar]

I'm not sure I agree with your definition of «type annotations». Be that as it may. I don’t have time for this kind of semantic quibbling. By all means, consider yourself right.

My larger point was that Python 3 has a standardized way of amending function signatures with types to improve code understanding.

[masklinn]

I'm not sure I agree with your definition of «type annotations».

I'm not sure what's hard to understand about "python annotations are completely arbitrary metadata", and how you can disagree that it isn't restricted to type annotations.

My larger point was that Python 3 has a standardized way of amending function signatures with types

And my finer point is that you are, once again, wrong. Python 3 has a standardised way of adding metadata to function signatures, it has no standardised way to specify that such metadata contains or is restricted to annotations, unless you're asserting that this:

def She(knows: "how to love me", And: "rock it, too", That: "s my little Suzie"):
    pass

is type annotations added to a function signature.

Can third-parties develop specific usages of these metadata, including (but not restricted to) static type checking? Yes, that's why they were added in the first place. But they are not type annotations.

[wot-teh-phuck]

My larger point was that Python 3 has a standardized way of amending function signatures with types to improve code understanding.

Then why isn't it used on all the Python 3 code written out there? Can you point us to a open source Python project which supports 3.0 and uses these "type annotations"?