Python isalpha, insumeric and isalnum(): A complete Guide

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Python isalpha, insumeric and isalnum(): A complete Guide
vinaykhatri

Vinay Khatri
Last updated on May 30, 2024

    The Python isalpha() , isnumeric() and isalnum() are three string methods that return boolean value True is the string only containing alphabets, numbers, and alphabets & numbers, respectively.

    While working with Python string values, we often come across situations where we need to perform some action based on the data value present in the string. For instance, we want to convert a string value into an integer if the string only contains a numeric value. Or you want to check if the username string value entered by the user is a valid input with no special characters. For such string value checks, we have three methods for Python string, isalpha() , isnumeric() and isalnum() . In this tutorial, we will walk through these three Python methods and learn how to use them. So let's get started.

    Python string isalpha() method

    The isalpha() method stands for "is alphabets?", this method returns a boolean value True if all the characters inside the string value are alphabets. Even if a single character inside the string value is a non-alphabet, such as white space, numeric value and special symbols, the method will return False

    Syntax

    string.isalpha()

    The isalpha() does not accept any argument and returns a Boolean value (True or False).

    Example

    string1 = "ThisStringContainsOnlyAlphabets"   #True
    string2 = "This string contains alphabets > symbol and white space"   
    string3 = "This string contains alphabets and numbers 1234" #False
    string4 = "12345"    #False
    
    print("Is string1 all alphabets?: ", string1.isalpha())
    print("Is string2 all alphabets?: ", string2.isalpha())
    print("Is string3 all alphabets?: ", string3.isalpha())
    print("Is string4 all alphabets?: ", string4.isalpha())

    Output

    Is string1 all alphabets?: True
    Is string2 all alphabets?: False
    Is string3 all alphabets?: False
    Is string4 all alphabets?: False

    Python string isnumeric() method

    The isnumeric() string method stands for "is numeric?". This method does not accept any argument value and returns a boolean value True or False after checking the string. The method isnumeric() returns True if all the characters inside the string are numbers. If any of the characters inside the string is an alphabet, special symbol, dot, or white space, the isnumeric() method will return False. Syntax

    string.isnumeric()

    Example

    string1 = "123,453" #False containing ,
    string2 = "1 234 567" #False containing white space
    string3 = "123.34" #False containing .
    string4 = "12345" #True all numbers
    
    print("Is string1 all Numbers?: ", string1.isnumeric())
    print("Is string2 all Numbers?: ", string2.isnumeric())
    print("Is string3 all Numbers?: ", string3.isnumeric())
    print("Is string4 all Numbers?: ", string4.isnumeric())

    Output

    Is string1 all Numbers?: False
    Is string2 all Numbers?: False
    Is string3 all Numbers?: False
    Is string4 all Numbers?: True

    Python string isalnum() method

    The python isalnum() is a string method that stands for "is alphabets or numbers?". This method is a combination of isalpha() and isnumeric() . isalnum() also does not accept any argument value and return a boolean value after checking all the string characters. This method returns True if all the characters inside the string are either alphabets or numbers. If the string contains any character other than alphabets or numbers then this method returns False. syntax string.isalnum()

    Example

    string1 = "ABC"         #True all alphabets
    string2 = "1234"        #True all numbers
    string3 = "123ABCD"     #True alphabets and numbers
    string4 = "12345 ABC"   #False cotaining white space
    
    print("Is string1 all AlphaNumeric Values?: ", string1.isalnum())
    print("Is string2 all AlphaNumeric Values?: ", string2.isalnum())
    print("Is string3 all AlphaNumeric Values?: ", string3.isalnum())
    print("Is string4 all AlphaNumeric Values?: ", string4.isalnum())
    
    

    Output

    Is string1 all AlphaNumeric Values?: True
    Is string2 all AlphaNumeric Values?: True
    Is string3 all AlphaNumeric Values?: True
    Is string4 all AlphaNumeric Values?: False

    Conclusion

    isalpha(), isnumeric() and isalnum() are the three most used Python string's methods. These three methods are widely used in string data analysis, although for most of the string analysis we always prefer to use regular expression, but string methods like these save a lot of time and make it easy for us to check the data. The isalpha() checks if the string contains only alphabets characters, the isnumeric() method checks if all the characters are numbers and the isalnum() checks if the string only contains alphabets or numbers.

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