if __name__ == '__main__':
    str="good good study,day day up"
    print(str[::2])
    print(str[::-1])#倒数
    print(str[::-2])
    print(str[1:10:2])
    print(str[-10:-1])
    print(str.title())#首字母大写
    upper=str.upper()#大写转换
    print(upper)
    lower = str.lower()#小写转换
    print(lower)