Python中返回函数的完全指南

def outer_function():
    def inner_function():
        print("这是内部函数")
    return inner_function  # 返回内部函数，而不是调用它

my_func = outer_function()  # 获取返回的函数
my_func()  # 调用返回的函数

def power_factory(exponent):
    def power(base):
        return base ** exponent
    return power

square = power_factory(2)  # 创建平方函数
cube = power_factory(3)    # 创建立方函数

print(square(4))  # 输出16
print(cube(3))    # 输出27

def counter():
    count = 0
    def increment():
        nonlocal count
        count += 1
        return count
    return increment

counter1 = counter()
print(counter1())  # 1
print(counter1())  # 2

counter2 = counter()  # 新的计数器，独立计数
print(counter2())  # 1

def my_decorator(func):
    def wrapper():
        print("函数执行前")
        func()
        print("函数执行后")
    return wrapper

@my_decorator
def say_hello():
    print("Hello!")

say_hello()

def greet_factory(greeting):
    def greet(name):
        return f"{greeting}, {name}!"
    return greet

say_hello = greet_factory("Hello")
say_hi = greet_factory("Hi")

print(say_hello("Alice"))  # Hello, Alice!
print(say_hi("Bob"))      # Hi, Bob!

def calculator_factory():
    def add(x, y):
        return x + y
    def subtract(x, y):
        return x - y
    return add, subtract

add_func, sub_func = calculator_factory()
print(add_func(5, 3))    # 8
print(sub_func(10, 4))   # 6

def get_operation(op):
    if op == '+':
        def operation(a, b):
            return a + b
    elif op == '*':
        def operation(a, b):
            return a * b
    else:
        def operation(a, b):
            return 0
    return operation

add = get_operation('+')
multiply = get_operation('*')

print(add(2, 3))        # 5
print(multiply(2, 3))   # 6

def create_multipliers():
    return [lambda x: i * x for i in range(5)]  # 有问题的方式

multipliers = create_multipliers()
print([m(2) for m in multipliers])  # 期望[0,2,4,6,8]，实际[8,8,8,8,8]

def create_multipliers():
    return [lambda x, i=i: i * x for i in range(5)]  # 使用默认参数捕获当前值

multipliers = create_multipliers()
print([m(2) for m in multipliers])  # 正确输出[0,2,4,6,8]

def outer():
    large_data = [...]  # 大数据
    def inner():
        # 即使不需要，inner也持有large_data的引用
        return 42
    return inner

def cache(func):
    cached_data = {}
    def wrapper(*args):
        if args in cached_data:
            print("从缓存获取结果")
            return cached_data[args]
        print("计算并缓存结果")
        result = func(*args)
        cached_data[args] = result
        return result
    return wrapper

@cache
def expensive_computation(x):
    print(f"执行复杂计算: {x}")
    return x * x

print(expensive_computation(4))  # 计算并缓存
print(expensive_computation(4))  # 从缓存获取
print(expensive_computation(5))  # 计算并缓存