Day 17: Converting Numeric Grades to Letters with Robustness and Clarity

#challenge #python #beginners #programming

Welcome to Day 17 of the #80DaysOfChallenges journey! Today’s
challenge was a polished take on a classic: converting numeric grades to letter grades, emphasizing clean input handling, modern conditional logic, and Python 3.10+ match-case. This beginner-to-intermediate task gave me a solid workout in validation, control flow, and user-friendly program design. It felt like building a tiny, reliable grading assistant.

💡 Key Takeaways from Day 17: Robust Grade Converter

This challenge accepts both integer and decimal grades (like 89.5), validates input thoroughly, and uses match-case to map values to A–F letters. The output is simple, but the strength lies in the input loop, data cleaning, and readable branching. Let’s break down the essentials: robust input, match-case for clarity, and smooth user flow.

1. Robust Input: Ensuring a Valid Grade Every Time

The get_valid_grade function is the gatekeeper. It uses a while True loop to force a valid float between 0 and 100, handling both whole numbers and decimals:

while True:
    raw_input_value = input("Enter your grade (0–100): ").strip()

    try:
        grade = float(raw_input_value)
    except ValueError:
        print("That doesn't look like a number. Please enter a valid numeric grade.")
        continue

    if not (0 <= grade <= 100):
        print("Grade must be between 0 and 100. Try again.")
        continue

    return grade

I loved how resilient this is; strip() removes stray spaces, float() accepts 85 or 89.5 equally well. If the user types "abc" or "-5", it responds with a clear message and loops again, no crashes, no nonsense. This kind of input handling turns a fragile script into something you can actually trust.

2. match-case: Modern, Readable Conditional Branching

The convert_to_letter_grade function uses Python 3.10+ match-case with guard clauses to define grade ranges cleanly, replacing long if-elif chains:

match grade:
    case grade if 90 <= grade <= 100:
        return "A"
    case grade if 80 <= grade < 90:
        return "B"
    case grade if 70 <= grade < 80:
        return "C"
    case grade if 60 <= grade < 70:
        return "D"
    case grade if 0 <= grade < 60:
        return "F"
    case _:
        return None  # Signal invalid value

Each case is explicit and scannable. For example, 92 → "A", 79.9 → "C". The wildcard case _ acts as a safety net (though input validation already prevents invalid ranges). It’s like reading a grading policy in code form, clear, maintainable, and elegant.

3. Program Flow: A Friendly, Interactive Experience

The main loop lets users convert multiple grades and exit gracefully:

while True:
    grade_value = get_valid_grade()
    letter = convert_to_letter_grade(grade_value)
    print(f"Your letter grade is {letter}")

    again = input("Would you like to enter another grade? (y/n): ").strip().lower()
    if again != "y":
        print("Thanks for using the grade converter! Goodbye.")
        break

Small touches like emojis (Checkmark, Graduation cap), consistent formatting, and case-insensitive input ("Y", "yes", " y ") make it feel polished. The user isn’t just running code, they’re having a conversation with it.

🎯 Summary and Reflections

This challenge showed that even a simple conversion can teach big lessons in code quality. It made me focus on:

Input resilience: Loop + try/except + validation = unbreakable user entry.
Modern syntax: match-case for multi-condition logic that reads like a table.
User experience: Clear feedback, flexibility, and a touch of warmth turn functionality into delight.

The surprise? How much cleaner match-case made the logic feel. It’s like the code grew up. For extensions, I could add plus/minus grades (A-, B+), or read from a CSV to process an entire class.

Advanced Alternatives: Use dataclasses to bundle grade data, or build a GUI with tkinter for visual input. How do you handle grading logic in Python? Drop your approaches below!

🚀 Next Steps and Resources

Day 17 grounded me in robust input and modern control flow, setting up for more interactive challenges. If you're on the #80DaysOfChallenges train, how did you handle validation? Any match-case tips or UX tweaks? Share in the comments!