What is the Literal type?

Question

Accepted Answer

**Literal** restricts a type to **specific values**.

```python
from typing import Literal

# Basic usage
Status = Literal["pending", "active", "deleted"]

def update_status(status: Status) -> None:
    print(f"Status: {status}")

update_status("active")  # OK
update_status("deleted") # OK
# update_status("unknown")  # Type error!

# With FastAPI
from fastapi import FastAPI

app = FastAPI()

@app.get("/items/")
async def read_items(
    q: Literal["foo", "bar"] | None = None
):
    if q:
        return {"q": q}
    return {"q": None}

# Combining with Union
Priority = Literal["low", "medium", "high"]

class Task(BaseModel):
    title: str
    priority: Priority
    status: Literal["todo", "done"]

task = Task(title="Work", priority="high", status="todo")

# Enum alternative
from enum import Enum

class StatusEnum(str, Enum):
    PENDING = "pending"
    ACTIVE = "active"
    DELETED = "deleted"

def update_status(status: StatusEnum) -> None:
    print(status.value)
```

**Literal vs Enum:**
- `Literal`: simpler, no class definition.
- `Enum`: more features (iteration, methods).

Python: What is the Literal type?