第二章：基础语法

1. 变量与基本类型

Python 是动态类型语言，可通过注解增强可读性与静态检查（mypy）。

x: int = 42
name: str = "hackcha"
items: list[int] = [1, 2, 3]
empty: dict[str, float] = {}

2. 控制流

for i in range(3):
    print(i)

match status:
    case 200:
        print("ok")
    case 404:
        print("not found")
    case _:
        print("other")

3. 推导式

squares = [n * n for n in range(10) if n % 2 == 0]
unique = {c for c in "hello"}

4. 异常

try:
    1 / 0
except ZeroDivisionError as e:
    print(f"caught: {e}")
finally:
    print("cleanup")

优先捕获具体异常类型，避免裸露的 except:。