What is the typing.TypeAlias and when to use it?

Question

Accepted Answer

**TypeAlias** creates **readable names** for complex types.

```python
from typing import TypeAlias

# Simple alias
UserID: TypeAlias = int
JSON: TypeAlias = dict[str, any]

# Complex type
Handler: TypeAlias = Callable[[str, int], bool]
Result: TypeAlias = tuple[bool, str | None]

# With generics
from typing import TypeVar, Generic

T = TypeVar("T")
Response: TypeAlias = dict[str, T]

# Usage
def get_user(user_id: UserID) -> JSON:
    return {"id": user_id}

def register_handler(handler: Handler) -> None:
    handlers.append(handler)

# In function signatures
def process(
    data: JSON,
    callback: Handler
) -> Result:
    # ...
    return (True, None)

# Python 3.12+ syntax
type UserID = int
type JSON = dict[str, any]
```

**Benefits:**
- Self-documenting code.
- Easier refactoring.
- Better IDE support.

Python: What is the typing.TypeAlias and when to use it?