像写 Rust 一样写 Python！

def find_item(records, check):

def find_item(
  records: List[Item],
  check: Callable[[Item], bool]
) -> Optional[Item]:

def find_person(...) -> Tuple[str, str, int]:

def find_person(...) -> Dict[str, Any]:
    ...
    return {
        "name": ...,
        "city": ...,
        "age": ...
    }

@dataclasses.dataclass
class City:
    name: str
    zip_code: int


@dataclasses.dataclass
class Person:
    name: str
    city: City
    age: int


def find_person(...) -> Person:

enum Packet {
  Header {
    protocol: Protocol,
    size: usize
  },
  Payload {
    data: Vec<u8>
  },
  Trailer {
    data: Vec<u8>,
    checksum: usize
  }
}

fn handle_packet(packet: Packet) {
  match packet {
    Packet::Header { protocol, size } => ...,
    Packet::Payload { data } |
    Packet::Trailer { data, ...} => println!("{data:?}")
  }
}

@dataclass
class Header:
  protocol: Protocol
  size: int

@dataclass
class Payload:
  data: str

@dataclass
class Trailer:
  data: str
  checksum: int

Packet = typing.Union[Header, Payload, Trailer]
# or `Packet = Header | Payload | Trailer` since Python 3.10

def handle_is_instance(packet: Packet):
    if isinstance(packet, Header):
        print("header {packet.protocol} {packet.size}")
    elif isinstance(packet, Payload):
        print("payload {packet.data}")
    elif isinstance(packet, Trailer):
        print("trailer {packet.checksum} {packet.data}")
    else:
        assert False

def handle_pattern_matching(packet: Packet):
    match packet:
        case Header(protocol, size): print(f"header {protocol} {size}")
        case Payload(data): print("payload {data}")
        case Trailer(data, checksum): print(f"trailer {checksum} {data}")
        case _: assert False

Packet = Header | Payload | Trailer
PacketWithData = Payload | Trailer

import serde

...
Packet = Header | Payload | Trailer

@dataclass
class Data:
    packet: Packet

serialized = serde.to_dict(Data(packet=Trailer(data="foo", checksum=42)))
# {'packet': {'Trailer': {'data': 'foo', 'checksum': 42}}}

deserialized = serde.from_dict(Data, serialized)
# Data(packet=Trailer(data='foo', checksum=42))

Config = ConfigV1 | ConfigV2 | ConfigV3

class Database:
  def get_car_id(self, brand: str) -> int:
  def get_driver_id(self, name: str) -> int:
  def get_ride_info(self, car_id: int, driver_id: int) -> RideInfo:

db = Database()
car_id = db.get_car_id("Mazda")
driver_id = db.get_driver_id("Stig")
info = db.get_ride_info(driver_id, car_id)

from typing import NewType

# Define a new type called "CarId", which is internally an `int`
CarId = NewType("CarId", int)
# Ditto for "DriverId"
DriverId = NewType("DriverId", int)

class Database:
  def get_car_id(self, brand: str) -> CarId:
  def get_driver_id(self, name: str) -> DriverId:
  def get_ride_info(self, car_id: CarId, driver_id: DriverId) -> RideInfo:


db = Database()
car_id = db.get_car_id("Mazda")
driver_id = db.get_driver_id("Stig")
# Type error here -> DriverId used instead of CarId and vice-versa
info = db.get_ride_info(<error>driver_id</error>, <error>car_id</error>)

class Rectangle:
    @staticmethod
    def from_x1x2y1y2(x1: float, ...) -> "Rectangle":
    
    @staticmethod
    def from_tl_and_size(top: float, left: float, width: float, height: float) -> "Rectangle":

class Client:
  """
  Rules:
  - Do not call `send_message` before calling `connect` and then `authenticate`.
  - Do not call `connect` or `authenticate` multiple times.
  - Do not call `close` without calling `connect`.
  - Do not call any method after calling `close`.
  """
  def __init__(self, address: str):

  def connect(self):
  def authenticate(self, password: str):
  def send_message(self, msg: str):
  def close(self):

def connect(address: str) -> Optional[ConnectedClient]:
  pass

class ConnectedClient:
  def authenticate(...):
  def send_message(...):
  def close(...):

class ConnectedClient:
  def authenticate(...) -> Optional["AuthenticatedClient"]:

class AuthenticatedClient:
  def send_message(...):
  def close(...):

with connect(...) as client:
    client.send_message("foo")
# Here the client is closed

@dataclass
class NormalizedBBox:
  left: float
  top: float
  width: float
  height: float


@dataclass
class DenormalizedBBox:
  left: float
  top: float
  width: float
  height: float

@dataclass
class BBoxBase:
  left: float
  top: float
  width: float
  height: float

# Composition
class NormalizedBBox:
  bbox: BBoxBase

class DenormalizedBBox:
  bbox: BBoxBase

Bbox = Union[NormalizedBBox, DenormalizedBBox]

# Inheritance
class NormalizedBBox(BBoxBase):
class DenormalizedBBox(BBoxBase):

class NormalizedBBox(BboxBase):
  def __post_init__(self):
    assert 0.0 <= self.left <= 1.0
    ...

class BBoxBase:
  def as_normalized(self, size: Size) -> "NormalizeBBox":
  def as_denormalized(self, size: Size) -> "DenormalizedBBox":

class NormalizedBBox(BBoxBase):
  def as_normalized(self, size: Size) -> "NormalizedBBox":
    return self
  def as_denormalized(self, size: Size) -> "DenormalizedBBox":
    return self.denormalize(size)

class DenormalizedBBox(BBoxBase):
  def as_normalized(self, size: Size) -> "NormalizedBBox":
    return self.normalize(size)
  def as_denormalized(self, size: Size) -> "DenormalizedBBox":
    return self

class BBoxBase:
  def move(self, x: float, y: float) -> typing.Self: ...

class NormalizedBBox(BBoxBase):
  ...

bbox = NormalizedBBox(...)
# The type of `bbox2` is `NormalizedBBox`, not just `BBoxBase`
bbox2 = bbox.move(1, 2)

{
  let guard = mutex.lock(); // locked here
  ...
} // automatically unlocked here

let lock = Mutex::new(41); // Create a mutex that stores the data inside
let guard = lock.lock().unwrap(); // Acquire guard
*guard += 1; // Modify the data using the guard

mutex = Lock()

def thread_fn(data):
    # Acquire mutex. There is no link to the protected variable.
    mutex.acquire()
    data.append(1)
    mutex.release()

data = []
t = Thread(target=thread_fn, args=(data,))
t.start()

# Here we can access the data without locking the mutex.
data.append(2)  # Oops

import contextlib
from threading import Lock
from typing import ContextManager, Generic, TypeVar

T = TypeVar("T")

# Make the Mutex generic over the value it stores.
# In this way we can get proper typing from the `lock` method.
class Mutex(Generic[T]):
  # Store the protected value inside the mutex 
  def __init__(self, value: T):
    # Name it with two underscores to make it a bit harder to accidentally
    # access the value from the outside.
    self.__value = value
    self.__lock = Lock()

  # Provide a context manager `lock` method, which locks the mutex,
  # provides the protected value, and then unlocks the mutex when the
  # context manager ends.
  @contextlib.contextmanager
  def lock(self) -> ContextManager[T]:
    self.__lock.acquire()
    try:
        yield self.__value
    finally:
        self.__lock.release()

# Create a mutex wrapping the data
mutex = Mutex([])

# Lock the mutex for the scope of the `with` block
with mutex.lock() as value:
  # value is typed as `list` here
  value.append(1)