python中的高阶函数示例详解

# 将列表中的每个元素平方
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))
print(squared)  # [1, 4, 9, 16, 25]

# 使用普通函数
def square(x):
    return x**2

squared = list(map(square, numbers))

# 过滤出偶数
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
print(even_numbers)  # [2, 4, 6, 8, 10]

# 过滤出长度大于3的字符串
words = ["apple", "cat", "dog", "elephant"]
long_words = list(filter(lambda word: len(word) > 3, words))
print(long_words)  # ["apple", "elephant"]

from functools import reduce

# 计算乘积
numbers = [1, 2, 3, 4, 5]
product = reduce(lambda x, y: x * y, numbers)
print(product)  # 120

# 找出最大值
max_value = reduce(lambda x, y: x if x > y else y, numbers)
print(max_value)  # 5

# 按字符串长度排序
words = ["apple", "cat", "dog", "banana"]
sorted_words = sorted(words, key=len)
print(sorted_words)  # ['cat', 'dog', 'apple', 'banana']

# 按第二个字符排序
sorted_by_second = sorted(words, key=lambda x: x[1])
print(sorted_by_second)  # ['banana', 'cat', 'apple', 'dog']

# 函数作为参数
def apply_twice(func, value):
    """将函数应用两次"""
    return func(func(value))

result = apply_twice(lambda x: x * 2, 3)
print(result)  # 12 (3*2=6, 6*2=12)

# 函数作为返回值
def create_multiplier(factor):
    """创建一个乘法器函数"""
    def multiplier(x):
        return x * factor
    return multiplier

double = create_multiplier(2)
triple = create_multiplier(3)

print(double(5))  # 10
print(triple(5))  # 15

def timer_decorator(func):
    """计算函数执行时间的装饰器"""
    def wrapper(*args, **kwargs):
        import time
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} 执行时间: {end - start:.4f}秒")
        return result
    return wrapper

@timer_decorator
def slow_function():
    import time
    time.sleep(1)
    return "完成"

result = slow_function()  # 会自动打印执行时间