Python String isalnum() Method

The isalnum() method returns True if all characters in the string are alphanumeric (either alphabets or numbers). If not, it returns False.

Syntax:

str.isalnum()

Parameters:

No parameters.

Return Value:

Returns True if all characters in the string are alphanumeric and returns False even if one character is not alphanumeric.

The following example demonstrates isalnum() method.

Example: isalnum()

mystr = 'Hello123'
print(mystr.isalnum())

mystr = '12345'
print(mystr.isalnum())

mystr = 'TutorialsTeacher'
print(mystr.isalnum())

Output

True
True
True

The isalnum() method will return False if the string consists of whitespaces and symbols.

Example: isalnum()

mystr = 'Python is a programming language.'
print(mystr.isalnum())

mystr = '#1'
print(mystr.isalnum())

mystr = 'Hello\tWorld'
print(mystr.isalnum())

Output

False
False
False

The isalnum() method can be used to identify non-alphanumerics in a string, as shown below.

Example: Separate Non-alphanumeric

def printNonAlphanumeric(str):
	print('non-alphanumerics:', end='')
	for i in str:
		if(i.isalnum() == False):
			print(i,end=',')
            
printNonAlphanumeric('*@TutorialsTeacher #123')

Output

non-alphanumerics:*,@, ,#,

The following table lists difference among the isalpha(), isalnum(), and isidentifier() methods based on the given inputs:

Input String	isaplha()	isalnum()	isidentifier()
'123'	False	True	False
'$123'	False	False	False
'XYZ123'	False	True	True
'123XYZ'	False	True	False
'_123XYZ'	False	False	True
'_XYZ_123'	False	False	True
'-XYZ-123'	False	False	False
'.XYZ.123'	False	False	False