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())

Ture

print(str_2.isdigit())

False

print(str_3.isdigit())

False

#用isalpha判断是否字母

print(str_1.isalpha())   

False

print(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())   

Ture

print(str_2.isalnum())

Ture

print(str_1.isalnum())   

Ture