《Python编程入门》9.1 类型注解语法与 pyright / mypy

def add(a: int, b: int) -> int:
    return a + b

print(add(1, 2))          # 正常
print(add("x", "y"))      # 传 str 也能跑
print(add([1], [2]))      # 传 list 也能跑

3
xy
[1, 2]

name: str = "Alice"
scores: dict[str, int] = {"math": 95}
flag: bool

def greet(who: str, times: int = 1) -> str:
    return who * times

class Point:
    x: int
    y: int = 0

def average(nums: list[float]) -> float:
    return sum(nums) / len(nums)

index: dict[str, list[int]] = {"a": [1, 2]}

from typing import Optional, Union

def f1(x: Optional[int]) -> int:
    return x or 0

def f2(x: int | None) -> int:   # 3.10 起可用
    return x or 0

def f3(x: int | str) -> str:    # 多类型联合
    return str(x)

print(f1(None), f2(5), f3(3))

0 5 3

from typing import Any, Callable, Never, NoReturn

def apply(fn: Callable[[int], str], x: int) -> str:
    return fn(x)

def crash() -> NoReturn:
    raise RuntimeError("boom")

def impossible(x: Never) -> None: ...

a: Any = 1
a.whatever.you.want()   # 检查器不会报错——Any 关掉了检查

o: object = "hello"
# o.upper()             # 检查器会报错：object 没有 upper

print(apply(str, 42))

42

from typing import Literal, Final, Annotated

Mode = Literal["r", "w", "a"]          # 只能是这三个字面量之一
MAX_RETRY: Final = 3                   # 常量，不允许再赋值
Port = Annotated[int, "1-65535"]       # 给类型挂一段元数据

def open_file(path: str, mode: Mode) -> None:
    ...

open_file("a.txt", "r")
# open_file("a.txt", "x")              # 检查器报错：x 不在 Literal 里

from __future__ import annotations
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from .models import Order   # 只在检查时导入，运行时不执行

def process(order: Order) -> None:
    ...

pip install "mypy==2.4.0"
npm install -g "pyright@1.1.414"

def add(a: int, b: int) -> int:
    return a + b

result: str = add(1, 2)
value = add("x", "y")

sample.py:4:15 - error: Type "int" is not assignable to declared type "str"
  "int" is not assignable to "str" (reportAssignmentType)
sample.py:5:13 - error: Argument of type "Literal['x']" cannot be assigned to parameter "a" of type "int" in function "add"
  "Literal['x']" is not assignable to "int" (reportArgumentType)
sample.py:5:18 - error: Argument of type "Literal['y']" cannot be assigned to parameter "b" of type "int" in function "add"
  "Literal['y']" is not assignable to "int" (reportArgumentType)
3 errors, 0 warnings, 0 informations

sample.py:4: error: Incompatible types in assignment (expression has type "int", variable has type "str")  [assignment]
sample.py:5: error: Argument 1 to "add" has incompatible type "str"; expected "int"  [arg-type]
sample.py:5: error: Argument 2 to "add" has incompatible type "str"; expected "int"  [arg-type]
Found 3 errors in 1 file (checked 1 source file)

Success: no issues found in 1 source file

from typing import get_type_hints

def greet(name: str, times: int = 1) -> str:
    return name * times

print(greet.__annotations__)
print(get_type_hints(greet))

{'name': <class 'str'>, 'times': <class 'int'>, 'return': <class 'str'>}
{'name': <class 'str'>, 'times': <class 'int'>, 'return': <class 'str'>}

import annotationlib

def f(x: Later) -> None:      # Later 此刻还没定义
    ...

class Later: ...

print(annotationlib.get_annotations(f, format=annotationlib.Format.VALUE))

{'x': <class '__main__.Later'>, 'return': None}