python如何判断输入都是字母

str_1 = "123"str_2 = "Abc"str_3 = "123Abc"#用isdigit函数判断是否数字print(str_1.isdigit())Tureprint(str_2.isdigit())Falseprint(str_3.isdigit())False#用isalpha判断是否字母print(str_1.isalpha())    Falseprint(str_2.isalpha())Ture    print(str_3.isalpha())    False#isalnum判断是否数字和字母的组合print(str_1.isalnum())    Tureprint(str_2.isalnum())Tureprint(str_1.isalnum())    Ture