Count Vowels From a String in Python Using Recursive Method

Recursion, an intriguing concept in programming, allows us to solve complex problems by breaking them down into smaller, more manageable subproblems. In this blog post, we will learn how to Count Vowels From a String in Python Using Recursive Method.

Throughout this blog post, we will provide step by step explanation of the logic and operation of the code, enabling you to grasp the intricacies of the recursive technique. In addition to understanding the code, we will also discuss the benefits and considerations of using recursion in this tutorial. 

Recursive methods can be useful for solving complex problems. However, it’s important to consider the performance implications of recursion, as it can be less efficient than iterative approaches for some problems.

Python Program to Count Vowels From a String Using Recursive Method

def isVowel(ch):
    return ch.upper() in ['A', 'E', 'I', 'O', 'U']
def countVovels(str, n):
    if (n == 1):
        return isVowel(str[n - 1]);
    return (countVovels(str, n - 1) + isVowel(str[n - 1]))
str = "Python programming"
print(countVovels(str, len(str)))

Code Logic Explanation

  • Defining a function to check if a character is a vowel

First, we initiate the isVowel function that takes a single argument ch, representing a character. It checks if the uppercase version of ch exists in the list [‘A’, ‘E’, ‘I’, ‘O’, ‘U’], which contains all the uppercase vowels. If ch is a vowel, the function returns True; otherwise, it returns False.

  • Defining the countVowels function to count the number of vowels in a string 

Now, we use the countVowels function, which takes two arguments: str and n. The ‘str’ argument represents the input string, and n represents the current index being processed.

If n is equal to 1 (base case), the function checks if the character at index n – 1 in the string is a vowel by initiating the isVowel function with the character.

If n is not equal to 1 (recursive case), the function makes a recursive call to itself with n – 1 as the new index and adds the result of the recursive call to the result of checking if the character at index n – 1 is a vowel. 

  • Initialising the string and printing the result

The variable str is initialised with the string “Python programming” as an example.

The countVowels function is called with the input string str and the length of the string (len(str)) as arguments. lastly, the function returns the total count of vowels in the string and prints the result.


When the user provides an input string as “Python programming”, the program will count the number of vowels in the input string using recursion and return the total count. In this case, the output will be the count of vowels in the string which is 4.

There Are Multiple Ways to Count Vowels From a String

In addition to the above method, there are multiple ways to achieve the same result of counting the number of vowels in a string in Python. They are:

An iterative approach using a for loop, built-in String Methods to count the occurrences of specific characters or substrings within a string, Regular Expressions to match and count patterns within strings using the re module, using a conditional expression within a List Comprehension to filter out the vowels from the string and then find the length of the resulting list.

While all these methods can achieve the desired result, we preferred the recursive approach as it offers readability, Simplicity, Flexibility, and Reusability. It is also important to consider factors such as performance, memory usage, and stack limits when dealing with large strings or deeply nested recursive calls. In such cases, iterative or other efficient approaches may be more suitable. 

In this tutorial, the program demonstrates the use of recursion to count the number of vowels in a given string. We proceed by breaking down the problem into smaller subproblems and making recursive calls, using which the code efficiently calculates the count of vowels.

The isVowel function helps determine if a character is a vowel, while the countVowels function handles the recursive logic. This approach offers an alternative method for counting vowels and showcases the power and flexibility of recursion in solving problems. By understanding and applying this code, Python programmers can gain insights into recursion and its practical application in string-processing tasks.

FAQ – Count Vowels From a String in Python Using Recursive

Can I use the countVowels function for any string?

Yes, the countVowels function is designed to work with any string. You can pass any string as an argument to count the number of vowels it contains.

Are there any limitations to using recursion for counting vowels?

Recursion can lead to stack overflow errors if used with large strings, as it relies on creating a new function call for each recursive step. It is recommended to use recursion for problems with smaller input sizes. For larger strings, an iterative approach might be more suitable.

Can this code be used for languages other than English?

This code can be used for any language that uses the same set of vowels as English (‘A’, ‘E’, ‘I’, ‘O’, ‘U’).

What will happen when I input a number in this program?

If you input a number as a string, the code will treat each digit of the number as separate characters and count the vowels accordingly. For example, if you input the string “12345”, the code will count the vowels ‘a’ and ‘e’ since they are present in the string. However, if you input a number directly (not as a string), it will result in a TypeError because the ‘in’ operator is not supported for integers. The ‘isVowel()’ function expects a character as input, not a number.

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