一文带你深入了解python中的类型注解

# 变量的基础类型注解
age: int = 25
height: float = 1.75
is_student: bool = True
name: str = "Alice"

# 函数参数和返回值的基础类型注解
def add_numbers(a: int, b: int) -> int:
    return a + b

# Python 3.9+
numbers: list[int] = [1, 2, 3]

# Python 3.8 及以前
from typing import List
numbers: List[int] = [1, 2, 3]

# Python 3.9+
person: tuple[str, int] = ("Bob", 30)

# Python 3.8 及以前
from typing import Tuple
person: Tuple[str, int] = ("Bob", 30)

# Python 3.9+
student: dict[str, int] = {"Alice": 20, "Bob": 22}

# Python 3.8 及以前
from typing import Dict
student: Dict[str, int] = {"Alice": 20, "Bob": 22}

from typing import Any

def print_anything(value: Any):
    print(value)

# 示例 1：函数参数可能是整数或字符串
# Python 3.10 之前
from typing import Union

def process_value(value: Union[int, str]):
    if isinstance(value, int):
        return value * 2
    elif isinstance(value, str):
        return value.upper()

result1 = process_value(5)
result2 = process_value("hello")
print(result1)  # 输出: 10
print(result2)  # 输出: HELLO

# Python 3.10 及以后
def process_value_new(value: int | str):
    if isinstance(value, int):
        return value * 2
    elif isinstance(value, str):
        return value.upper()

# 示例 2：处理文件内容可能是字符串或字节
def read_file_content(file_path: str) -> Union[str, bytes]:
    try:
        with open(file_path, 'r') as f:
            return f.read()
    except UnicodeDecodeError:
        with open(file_path, 'rb') as f:
            return f.read()

from typing import Optional

def get_name() -> Optional[str]:
    # 可能返回字符串，也可能返回 None
    import random
    if random.choice([True, False]):
        return "Alice"
    return None

from typing import Callable

def apply(func: Callable[[int, int], int], a: int, b: int) -> int:
    return func(a, b)

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

result = apply(add, 1, 2)

# 示例 1：通用的查找最大值函数
from collections.abc import Sequence
from typing import TypeVar

T = TypeVar('T', bound=int | float)

def find_max(seq: Sequence[T]) -> T | None:
    if not seq:
        return None
    max_val = seq[0]
    for item in seq:
        if item > max_val:
            max_val = item
    return max_val

numbers = [1, 5, 3, 9, 2]
max_num = find_max(numbers)
print(max_num)  # 输出: 9

# 示例 2：通用的栈类
from typing import Generic, TypeVar

T = TypeVar('T')

class Stack(Generic[T]):
    def __init__(self):
        self.items: list[T] = []

    def push(self, item: T):
        self.items.append(item)

    def pop(self) -> T:
        return self.items.pop()

    def is_empty(self) -> bool:
        return len(self.items) == 0

# 创建一个存储整数的栈
int_stack = Stack[int]()
int_stack.push(1)
int_stack.push(2)
print(int_stack.pop())  # 输出: 2

# 创建一个存储字符串的栈
str_stack = Stack[str]()
str_stack.push("hello")
str_stack.push("world")
print(str_stack.pop())  # 输出: world

from collections.abc import Sequence

def my_sort(seq: Sequence[T]) -> Sequence[T]:
    return sorted(seq)

numbers = [3, 1, 2]
sorted_numbers = my_sort(numbers)

strings = ["banana", "apple", "cherry"]
sorted_strings = my_sort(strings)

def process_value(value: int | str):
    if isinstance(value, int):
        print(f"The integer value is {value}")
    else:
        print(f"The string value is {value}")

process_value(10)
process_value("hello")

x: int = 10
x = "hello"  # 虽然有类型注解，但代码仍然可以正常运行，因为类型注解不影响运行时行为

from typing import List

# 定义类型别名
Vector = List[float]

def scale_vector(vector: Vector, factor: float) -> Vector:
    return [i * factor for i in vector]

pip install mypy
mypy your_script.py

class Person:
    name: str
    age: int

    def __init__(self, name: str, age: int):
        self.name = name
        self.age = age

    def get_info(self) -> str:
        return f"{self.name} is {self.age} years old."