Starting with Python 3.9, you can use list[str] as a type annotation, which doesn't require importing anything, as documented in PEP 585.

Python 3.5 standardizes the way function annotations are used for type hinting, as documented in PEP 484. To annotate a list of strings, you use List[str], where List is imported from the typing module. You can also use Sequence[str] if your function accepts any list-like sequence, or Iterable[str] for any iterable.

Python 3.4 and earlier doesn't specify a format for its function annotations, it merely provides a mechanism that allows you to use any expression as the annotation. How the annotations are interpreted is up to you and the libraries you use.

Annotated in python allows developers to declare the type of a reference and provide additional information related to it.

name: Annotated[str, "first letter is capital"]

This tells that name is of type str and that name[0] is a capital letter.

On its own Annotated does not do anything other than assigning extra information (metadata) to a reference. It is up to another code, which can be a library, framework or your own code, to interpret the metadata and make use of it.

For example, FastAPI uses Annotated for data validation:

def read_items(q: Annotated[str, Query(max_length=50)])

Here the parameter q is of type str with a maximum length of 50. This information was communicated to FastAPI (or any other underlying library) using the Annotated keyword.