Python: Count Lines Containing a Specific Word (Solved)

Practice Question 29

In this question, we will learn how to write a function that scans a report and counts how many individual lines mention the word “success”. This is a common task in log analysis and data filtering.

The Logic (How it works)

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

We use a list-based approach to ensure we check every line individually:

• The readlines() Method: We read the entire file into a list where each element is one line from the file.

• The in Operator: This is a membership operator that checks if a string exists anywhere inside another string.

• Case Insensitivity: Since “Success” and “success” are different to a computer, we use .lower() to make the search uniform.

• The Counter: If the word exists in the line, we increment the count.

Let’s Code as per the above logic :

def countLinesWithWord():
    f = open("report.txt", "r")
    linelist = f.readlines()
    count = 0
    
    for line in linelist:
        # Using .lower() ensures we find "Success", "SUCCESS", and "success"
        if "success" in line.lower():
            count += 1
            
    f.close()
    return count

# To call the function and see the result:
print("Number of lines containing 'success':", countLinesWithWord())

Important Notes for Students

As a teacher, I want you to focus on these three key points so you don’t lose marks:

• Line-Based Counting: This code counts the line. If “success” appears twice on the same line, the count only goes up by 1 for that line.

• readlines() vs read(): While read() gives you one giant string, readlines() gives you a structured list of lines, which is perfect when the question specifically asks you to “count lines.”

• Substring Match: The in operator finds the word even if it’s part of another word (like “successfully”).

Teacher’s Secret Tip for Exams:

When searching for a word in a line, there are usually 3 specific cases the examiner might ask you to handle:

• Starts with: if line.lower().startswith("success"):

• Ends with: if line.lower().endswith("success"):

• Anywhere in between: if "success" in line.lower(): (This is what we used above!)

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]