如何在递归函数中只定义和初始化变量一次？

def recursive_function(n):
    # 定义静态变量
    static_var = getattr(recursive_function, 'static_var', None)
    if static_var is None:
        static_var = 0
        recursive_function.static_var = static_var

    # 递归终止条件
    if n == 0:
        return static_var

    # 递归调用
    static_var += 1
    return recursive_function(n-1)

# 测试递归函数
result = recursive_function(5)
print(result)  # 输出：5