Evolution of Type Hints in Python — From Comments to Inline Typing and Beyond

# Python 3.5 (PEP 484)
from typing import List

def greet_all(names: List[str]) -> None:
    for name in names:
        print(f"Hello, {name}!")
````

This basic form of static typing opened the door for tools like **mypy**, **pyright**, **pylance** and most recently **ty**, **pyrefly** to provide editor-level correctness checks.

This basic form of static typing opened the door for tools like [**mypy**](https://mypy-lang.org/), [**pyright**](https://github.com/microsoft/pyright), [**pylance**](https://marketplace.visualstudio.com/items?itemName=ms-python.vscode-pylance), and most recently [**ty**](https://docs.astral.sh/ty/), [**pyrefly**](https://pyrefly.org/) to provide editor-level correctness checks.

## Key Features Through Versions

### Python 3.5 (PEP 484) — The Birth of Typing

Introduced the `typing` module:

- `List`, `Dict`, `Tuple`, `Optional`, `Union`
- `Callable`, `Any`, `TypeVar`, `Generic`
- Function annotations became official.

### Python 3.6 — Variable Annotations

You could finally type variables directly without using comments:

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Also introduced `typing.NamedTuple` and `typing.NewType`.

### Python 3.7 — Postponed Evaluation (PEP 563)

Type hints were treated as **strings** by default (via `from __future__ import annotations`), delaying their evaluation until runtime.  
This solved circular import issues and reduced overhead in function definitions.

### Python 3.8 — TypedDict and Literal Types

Added:

- `TypedDict` for describing dicts with specific key/value types.
- `Final` and `Literal` for immutability and constant values.
- `Protocol` (PEP 544) for structural subtyping.

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### Python 3.9 — Built-in Generics (PEP 585)

This was a huge quality-of-life upgrade:  
`list[int]` replaced `List[int]`, `dict[str, int]` replaced `Dict[str, int]`.

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### Python 3.10 — Union Operator (PEP 604)

Simplified `Union` syntax using the `|` operator.

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Also improved type narrowing in `match` statements (structural pattern matching).

### Python 3.11 — Self Type, Variadic Generics, TypedDict Enhancements

- `Self` for methods returning their own type (PEP 673).
- `TypeVarTuple` and `Unpack` for variadic generics (PEP 646).
- `NotRequired` and `Required` for `TypedDict` fields.

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### Python 3.12 — The `typing` Cleanup

Deprecated old-style generics (`List`, `Dict`, etc.).  
Introduced `TypeAliasType` (PEP 695) and made `type` annotations simpler:

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### Python 3.13 — No More `from __future__ import annotations`

Postponed evaluation of annotations is now **default**, removing one of the last confusing steps in typing setup.

## Useful Patterns

### Simplified Union Types

Readable and concise unions are now idiomatic:

```python
def load_data(source: str | Path) -> str: ...

from typing import Protocol

class SupportsClose(Protocol):
    def close(self) -> None: ...

def cleanup(obj: SupportsClose) -> None:
    obj.close()

class Config(TypedDict, total=False):
    host: str
    port: int

class Query:
    def where(self, condition: str) -> Self:
        ...
    def execute(self) -> None:
        ...