Python | Extract Strings with only Alphabets

Last Updated : 13 Jan, 2025

In Python, extracting strings that contain only alphabetic characters involves filtering out any strings that include numbers or special characters.

The most efficient way to achieve this is by using the isalpha() method, which checks if all characters in a string are alphabetic.

Python

li= ['gfg', 'is23', 'best', 'for2', 'geeks']  
res = [sub for sub in li if sub.isalpha()] 
print(str(res))

Output

['gfg', 'best', 'geeks']

Explanation:

sub.isalpha() method is used to check if a string consists only of alphabetic characters. It returns True if the string contains only letters no numbers or special characters , otherwise it returns False.
List comprehension loops through each element of the list li and checks if it passes the isalpha() test.

Table of Content

Using filter()
Using regular expressions
Using all()

Using filter()

filter() function uses str.isalpha() to check if each string contains only alphabetic characters, filtering the list accordingly. The result is an iterator, which can be converted to a list. It's efficient but less intuitive than list comprehension.

Python

li= ['gfg', 'is23', 'best', 'for2', 'geeks']
res = list(filter(str.isalpha, li))
print(res)

Output

['gfg', 'best', 'geeks']

Explanation:

str.isalpha checks if each string in the list contains only alphabetic characters .
filter() goes through each item in the list li and applies the str.isalpha() condition:
list(filter(str.isalpha, li)): Since filter() returns an iterator, we need to convert it to a list using list() to get the filtered results.

Using regular expressions

This method uses regular expressions to match strings that contain only alphabetic characters. While regular expressions are versatile and powerful, they might be slightly slower than isalpha() for this simple task due to the overhead of regex processing.

Python

import re
li = ['gfg', 'is23', 'best', 'for2', 'geeks']
res = [sub for sub in li if re.match('^[a-zA-Z]+$', sub)]
print(res)

Output

['gfg', 'best', 'geeks']

Explanation:

re.match('^[a-zA-Z]+$', sub): This is where a regular expression is used to check if a string sub contains only alphabetic characters.
List comprehension loops through each string in the list li and applies the re.match() function.

Using all()

all() function can be used in list comprehension to check if every character in a string is alphabetic. It iterates over each character and applies isalpha() to ensure all characters are letters.

Python

li = ['gfg', 'is23', 'best', 'for2', 'geeks']
res = [sub for sub in li if all(c.isalpha() for c in sub)]
print(res)

Output

['gfg', 'best', 'geeks']

Explanation:

(all(c.isalpha() for c in sub)):This checks if every character in sub is alphabetic using c.isalpha()
all(): This ensures all characters in sub are alphabetic.
If all characters are alphabetic it returns True, otherwise False.