How To Check If A String Is Only Letters Python

In this tutorial, we will learn how to check if a given string consists of only letters in Python. We will look into different approaches such as using built-in methods, regex, and more to achieve this.

Checking if a string contains only letters is a common task in programming, which often comes in handy in data validation or preprocessing.

Step 1: Using the .isalpha() method

Python’s built-in method str.isalpha() is used to check if all the characters in the given string are alphabetic (letters). The method returns True if all characters are letters, and False otherwise. Here’s how to use the isalpha() method:

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def is_only_letters(string):
    return string.isalpha()
 
input_string = "HelloWorld"
result = is_only_letters(input_string)
print(result)

Output:

True

Step 2: Using Regular Expressions

Alternatively, we can use regular expressions to check if a string contains only letters. This method is more powerful and flexible, as it allows for more complex patterns. To apply this method, we will use the re module.

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import re
 
def is_only_letters(string):
    pattern = "^[A-Za-z]+$"
    return bool(re.match(pattern, string))
 
input_string = "HelloWorld123"
result = is_only_letters(input_string)
print(result)

Output:

False

The ^ character indicates the start of the line, while the $ character signifies the end of the line. [A-Za-z] represents a character within the English alphabet (both uppercase and lowercase).

The + means one or more occurrences of the preceding pattern. So, the whole pattern “^[A-Za-z]+$” translates to “a string consisting only of one or more English letters.” The re.match() method checks if the given string matches this pattern.

Step 3: Using List Comprehension and .isalpha() method

Another approach is to use list comprehensions to create a list of all characters in the string that are letters using isalpha(), and then check if the length of this list is equal to the length of the original string.

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def is_only_letters(string):
    letters = [char for char in string if char.isalpha()]
    return len(letters) == len(string)
 
input_string = "HelloWorld!!!"
result = is_only_letters(input_string)
print(result)

Output:

False

Conclusion

In this tutorial, we learned three different approaches to checking if a string consists of only letters in Python, including the simple .isalpha() method, regex, and list comprehension.

Depending on the desired flexibility and application, you may choose the method that fits your needs the best.