What is the typing.overload decorator?

Question

Accepted Answer

**@overload** defines **multiple signatures** for a function (for type checkers).

```python
from typing import overload

@overload
def process(value: int) -> int: ...

@overload
def process(value: str) -> str: ...

@overload
def process(value: list) -> list: ...

def process(value):
    if isinstance(value, int):
        return value * 2
    elif isinstance(value, str):
        return value.upper()
    elif isinstance(value, list):
        return [process(item) for item in value]
    raise TypeError(f"Unsupported type: {type(value)}")

# Type checker understands:
process(5)         # returns int
process("hello")   # returns str
process([1, 2])    # returns list

# With FastAPI
from fastapi import FastAPI

app = FastAPI()

@overload
async def get_user(user_id: int) -> User: ...

@overload
async def get_user(email: str) -> User: ...

async def get_user(user_id_or_email):
    if isinstance(user_id_or_email, int):
        return await db.get(User, user_id_or_email)
    return await db.get(User, email=user_id_or_email)
```

**Rules:**
- Must have at least 2 overloads.
- Implementation has no annotations.
- Used only by type checkers (mypy, pyright).

Python: What is the typing.overload decorator?