Character tests: isdigit(), isalpha(), isalnum(), isspace(), isupper(), islower()

Strings have a family of methods beginning with is that test what kind of characters the string contains. Each returns True or False and never changes the string. They are ideal for validating input before converting or storing it. They share two rules that exam questions probe: the test applies to every character in the string, and an empty string returns False for all of them.