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

By | November 17, 2021
Python isalpha, insumeric and isalnum()

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

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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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