Question 241 markShort AnswerSection B

$A statement to check whether the given character, ch is an alphabet or a number.$

Q: A statement to check whether the given character, ch is an alphabet or a number.

**Required statement:** ```python print(ch.isalnum()) ``` The built-in string method `isalnum()` returns `True` if the character `ch` is either an alphabet letter or a digit, and `False` otherwise.

Python Revision Tour

Checking Alphanumeric Characters — isalnum()

Official answer

Required statement: `` python print(ch.isalnum()) ` The built-in string method isalnum() returns True if the character ch is either an alphabet letter or a digit, and False` otherwise.

isalnum()

isalpha()

isdigit()

string methods

character classification

alphanumeric check

built-in function

Marking scheme

1. $1 mark for the correct statement `print(ch.isalnum())`; the equivalent `ch.isalpha() or ch.isdigit()` is also accepted.$

Hint

$Look for the single string method whose name literally combines 'alphabet' and 'number' — alnum.$

Quick oral answer

$ch.isalnum() returns True if ch is a letter or a digit, giving a single built-in check for whether a character is alphanumeric.$

Common mistakes

1. $Using only `ch.isalpha()`, which checks for alphabets alone and incorrectly returns False for a digit character.$
2. $Forgetting that these string methods only work correctly on a SINGLE character string when checking one character; on multi-character strings they check that ALL characters satisfy the condition.$

Analysis and explanation

This question tests knowledge of Python's built-in character-classification string methods. Why ch.isalnum() is correct isalnum() checks whether every character in the string is alphanumeric — meaning it is a letter (A-Z, a-z) OR a digit (0-9). Since ch is a single character, ch.isalnum() directly answers 'is ch an alphabet or a number?' in one built-in call. Equivalent alternative The same check can also be written as ch.isalpha() or ch.isdigit(), which combines two separate built-in methods with a logical OR, giving an identical True/False result.

Interesting facts

$`isalnum()` returns False for an empty string, since there is no character to satisfy the check — this edge case is a favourite CBSE viva question.$

$Python's `str.isalnum()` also returns True for many Unicode numeric and alphabetic characters beyond plain ASCII, such as accented letters and superscript digits.$

Question details

Q24 of 48 questions

Board: CBSE
Class: Class 12
Subject: Computer Science
Year: 2026
Section: Section B
Marks: 1
Type: Short Answer
Chapter: Python Revision Tour
Topic: $Checking Alphanumeric Characters — isalnum()$
Bloom's level: apply
Syllabus topic: $Unit 1: Computational Thinking and Programming — Strings (Built-in Method: isalnum())$
Author: CBSE
Reviewed by: Padhantu Academic Team

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Frequently asked questions

$What does ch.isalnum() return for a space character?$

$It returns False, since a space is neither an alphabet letter nor a digit.$

$Can isalpha() or isdigit() be used instead of isalnum()?$

$Yes, `ch.isalpha() or ch.isdigit()` gives the same True/False result as `ch.isalnum()` for a single character.$