Day 15: Mini Project + Recap

Quick Answer

What You Will Learn

• calc(a, op, b) takes two numbers and an operator and returns the result.
• Division by zero is checked first, so the program returns a message instead of crashing.
• A dictionary maps each operator to its job, using a small lambda function for each.
• ops[op]() picks the right operation from the dictionary and runs it; an unknown operator gives 'Invalid op'.
• The guessing game compares each guess with the secret and breaks out of the loop on a correct guess.
• Top 3 beginner mistakes: = vs ==, forgetting int() on input(), and wrong indentation.

Code

def calc(a, op, b):
    if op == "/" and b == 0:
        return "Cannot divide by zero"
    ops = {"+": lambda: a + b, "-": lambda: a - b, "*": lambda: a * b, "/": lambda: a / b}
    return ops[op]() if op in ops else "Invalid op"

print(calc(8, "*", 5))
print(calc(8, "/", 0))
print(calc(10, "+", 5))
secret = 7
guesses = [3, 9, 7]
for guess in guesses:
    if guess == secret:
        print("Correct!")
        break
    print("Too high" if guess > secret else "Too low")

Output

40
Cannot divide by zero
15
Too low
Too high
Correct!

Code Explained, Line by Line

1. calc(a, op, b) takes two numbers and an operator and returns the result.
2. Division by zero is checked first, so the program returns a message instead of crashing.
3. A dictionary maps each operator to its job, using a small lambda function for each.
4. ops[op]() picks the right operation from the dictionary and runs it; an unknown operator gives 'Invalid op'.
5. The guessing game compares each guess with the secret and breaks out of the loop on a correct guess.
6. Top 3 beginner mistakes: = vs ==, forgetting int() on input(), and wrong indentation.

Real-Life Use

Calculators and guessing games combine everything from Phase 1: variables, conditions, loops, lists and functions.

Test Yourself — MCQs

Select (tick) an option, then tap Check answer to see instantly whether your answer is right or wrong, with an explanation. You can change your answer and check again.

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