Python: Calculate Sum of All Digits in a Text File (Solved)

Practice Question 3

In this post, we will learn how to write a function that finds all the numerical digits in a text file and calculates their sum. This is a fantastic exercise for learning how to extract numbers from a mix of text and symbols

The Logic (How it works)

Before writing the code, let us first understand the logic behind the solution.

When we read a file, everything—including numbers—is treated as a “string.” To add them up, we need to follow these steps:

• Open & Read: We open letter.txt and read the content.

• Identify Digits: We look at every character and check if it is a number using .isdigit().

• Type Conversion: Since you cannot mathematically add a “string” number, we convert the character into an integer using int().

• Running Total: We add that integer to a total_sum variable.

Let’s Code as per the above logic :

def sumOfDigits():
    f = open("letter.txt", "r")
    data = f.read()
    total_sum = 0
    
    for alpha in data:
        if alpha.isdigit():
            total_sum += int(alpha)
            
    f.close()
    return total_sum

# To call the function and see the result:
print("The sum of all digits is:", sumOfDigits())

Important Notes for Students

As a teacher, I want you to pay close attention to these two points, as they are where most students make mistakes in exams:

1. Why use int()? In Python, the character '5' from a file is a string, not a number. If you try to add it without int(), Python will give you a “TypeError.” Converting it to an integer allows us to perform addition.

2. The isdigit() Method: This is a built-in string method that returns True only if the character is a digit (0-9). It automatically ignores alphabets, spaces, and special symbols for us.

3. Variable Initialization: Always remember to set your total_sum = 0 outside the loop. If you put it inside the loop, the sum will reset to zero every time a new character is read!

Teacher’s Secret Tip for Exams:

This logic is very flexible! Depending on what the question asks, you only need to change one line:

• To Count Digits: Use total_sum += 1 instead of adding the value.

• To Display Digits: Simply use print(alpha) inside the if condition.

• To Sum Digits: Use total_sum += int(alpha) as shown in the solution above.

Learning how to tweak one logic for different goals is the secret to becoming a great programmer!

Want to practice more? If you found this helpful, I have compiled a full list of 30 practice problems just like this one. Each question focuses on a different logic to help you become a pro at File Handling.

Click here to view the full 30-Question Practice Set

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