In Python, the str.isalnum() method is used to check if all characters in a string are alphanumeric, meaning that they are either letters (a-z, A-Z) or digits (0-9). This method returns True if the string contains at least one character and all characters are alphanumeric; otherwise, it returns False.

Syntax

str.isalnum()

Example Usage

1. Basic usage with letters and digits:

text = "Hello123"
result = text.isalnum()
print(result)  # Output: True

2. Including spaces:

text = "Hello 123"
result = text.isalnum()
print(result)  # Output: False (space is not alphanumeric)

3. With special characters:

text = "Hello@123"
result = text.isalnum()
print(result)  # Output: False (the '@' is not alphanumeric)

4. Checking an empty string:

text = ""
result = text.isalnum()
print(result)  # Output: False (empty string has no characters)

5. Using non-English alphanumeric characters:

text = "Café123"
result = text.isalnum()
print(result)  # Output: True (accented 'é' is considered a letter)

6. Only letters:

text = "HelloWorld"
result = text.isalnum()
print(result)  # Output: True (all letters)

7. Only digits:

text = "12345"
result = text.isalnum()
print(result)  # Output: True (all digits)

Important Notes

• The isalnum() method will return False if the string contains any characters that are not letters or digits, including whitespace and punctuation.
• It considers Unicode characters as well, so letters from various languages and scripts are included as valid alphanumeric characters.

Summary

• Use str.isalnum() to check if a string consists entirely of alphanumeric characters.
• It returns True for strings made up of letters and digits (including accented characters) and False for strings that contain any non-alphanumeric characters.