python有三种字符串占位符方式，代码演示如下：

if __name__ == "__main__":
    name = "Lucy"
    age = 20
    # 方式一：占位符,%s表示只能接受string, %d代表只能接受数字
    print("name is %s and age is %d" % (name, age))
    # format的用法1，需要用{n}作占位符，占位符从0开始
    print("name is {0} and age is {1}".format(name, age))
    # format的用法2，需要用{alias(别名)}作占位符
    print("name is {_name} and age is {_age}".format(_name=name, _age=age))

输出：

name is Lucy and age is 20
name is Lucy and age is 20
name is Lucy and age is 20