Which of the following functions cannot be used with string(str) data type?

Answer: isnum() is not a valid string method in Python.

Explanation: The methods islower(), isupper(), and isalpha() are valid string methods. There is no built-in method named isnum(). To check whether a string contains numeric characters, use isnumeric(), isdigit(), or isdecimal() depending on the need.

• islower(): Returns True if the string has at least one cased character and all such characters are lowercase. Example: "hello".islower() -> True

• isupper(): Returns True if the string has at least one cased character and all such characters are uppercase. Example: "HELLO".isupper() -> True

• isalpha(): Returns True if all characters are alphabetic and the string is non-empty. Example: "abc".isalpha() -> True; "abc123".isalpha() -> False

• isnum(): This name is not a valid str method. Use isnumeric(), isdigit(), or isdecimal() to test numeric content. Example: "123".isnumeric() -> True

Therefore, the function that cannot be used with the string (str) data type is isnum().