python/day03/functions_basics.py

"""functions_basics.py - Python 函数基础示例

涵盖：普通函数、参数、返回值、默认参数、关键字参数、可变参数、
匿名函数、递归函数、作用域和闭包基础等。
类变量和实例变量的查找顺序

"""


def greet(name):
    """普通函数：接收参数并返回字符串。"""
    return f"Hello, {name}!"


def add(a, b):
    """普通函数：求和。"""
    return a + b


def power(base, exponent=2):
    """默认参数：exponent 默认值为 2。"""
    return base ** exponent


def show_student(name, age, city="Beijing"):
    """默认参数示例。"""
    print(f"Name: {name}, Age: {age}, City: {city}")


def print_info(name, *, age, city):
    """keyword-only 参数：必须使用关键字传参。"""
    print(f"{name}, {age}, {city}")


def sum_all(*numbers):
    """可变参数：接收任意数量的位置参数。"""
    total = 0
    for n in numbers:
        total += n
    return total


def print_scores(**scores):
    """关键字可变参数：接收任意数量关键字参数。"""
    for key, value in scores.items():
        print(f"{key} = {value}")


def factorial(n):
    """递归函数：阶乘。"""
    if n == 1 or n == 0:
        return 1
    return n * factorial(n - 1)


def outer():
    """闭包示例：内部函数访问外部变量。"""
    x = 10

    def inner():
        return x + 5

    return inner

inner2 = outer()  # outer() 返回 inner 函数对象
print("inner() ->", inner2())  # 调用 inner 函数

# 匿名函数（lambda）
square = lambda x: x * x
# lambda 参数列表: 表达式
# f = lambda x, y: x + y
# f(2,3)  # 返回 5

# 全局变量与局部变量
count = 0


def increase():
    global count
    count += 1
    return count


# 默认参数注意事项：不要使用可变对象作为默认值
# 例如：def append_item(items=[]): ...


def main():
    print("greet('Tom') ->", greet("Tom"))
    print("add(3, 5) ->", add(3, 5))
    print("power(3) ->", power(3))
    print("power(3, 3) ->", power(3, 3))

    show_student("Alice", 18)
    show_student("Bob", 20, "Shanghai")

    print_info("Tom", age=25, city="Hangzhou")

    print("sum_all(1, 2, 3, 4) ->", sum_all(1, 2, 3, 4))
    print_scores(math=90, english=88, history=94)

    print("factorial(5) ->", factorial(5))

    closure = outer()
    print("closure() ->", closure())

    print("square(6) ->", square(6))
    print("increase() ->", increase())
    print("increase() ->", increase())

    # 函数作为参数传递
    def do_math(x, func):
        return func(x)

    print("do_math(8, square) ->", do_math(8, square))


# 三元表达式
x = 1
y = 2
result = x if x > y else y

if __name__ == '__main__':
    main()