Python Build a Calculator with Functions

This guide explains build a calculator with functions through a focused Python example. You will learn the behavior to expect, why it matters in a real program, and how to recognize the common mistakes before applying it in your own project.

What You Will Learn

A calculator is a good example of small functions that each handle one operation. Separate calculation from input collection so the arithmetic can be tested without typing.

When and Why to Use It

The following example focuses on a practical use of Build a Calculator with Functions.

Step-by-Step Example

def calculate(first_number, operator, second_number):
    if operator == "+":
        return first_number + second_number
    if operator == "-":
        return first_number - second_number
    if operator == "/":
        if second_number == 0:
            raise ValueError("Cannot divide by zero")
        return first_number / second_number
    raise ValueError("Unsupported operator")

print(calculate(12, "/", 3))

Understanding the Example

The example returns 4.0 for division. Unrecognized operators and zero divisors produce controlled errors rather than misleading results.

Expected Output

4.0

Important Behavior and Edge Cases

Avoid eval on arbitrary user-provided expressions. A whitelist of supported operators is easier to understand and safer.

Try It Yourself

Add multiplication and test one supported and one unsupported operator.

Common Beginner Mistakes

• Avoid eval on arbitrary user-provided expressions. A whitelist of supported operators is easier to understand and safer.
• Confusing a returned value with printed output, or failing to verify a function’s behavior with different input values.
• Skipping the practice step and assuming the example covers every input. Test at least one normal case and one edge case relevant to this topic.

Key Takeaways

• A calculator is a good example of small functions that each handle one operation.
• The example returns 4.0 for division.
• Apply the technique deliberately, checking its documented input requirements and failure behavior before integrating it into a larger project.