Unit 10 • Lesson 6

Error Handling and Testing Your Code

Overview

Before final submission, your project must run without crashing. You'll use exception handling, debugging techniques, and testing strategies to make sure your program behaves as expected, ensuring reliability and professionalism.

Intermediate 30–40 min

Next: Polishing with Visuals or Output Formatting All Units

What You Will Learn in This Lesson

By the end of this lesson, you will know:

Error handling: Using try-except to handle errors gracefully.
Testing: Verifying your code works correctly.
Debugging: Finding and fixing bugs.
Edge cases: Testing unusual inputs and situations.
Reliability: Making your project robust and professional.

Why Error Handling Matters

Programs that handle errors gracefully:

Don't Crash

Handle errors instead of stopping unexpectedly

Provide Feedback

Tell users what went wrong and how to fix it

Are More Reliable

Work correctly even with unexpected input

Are Professional

Show attention to detail and user experience

Using Try-Except

Use try-except blocks to handle errors:

Error Handling Examples

# Basic error handling
try:
    number = int(input("Enter a number: "))
    result = 10 / number
    print(f"Result: {result}")
except ValueError:
    print("Error: Please enter a valid number.")
except ZeroDivisionError:
    print("Error: Cannot divide by zero.")

# File handling with errors
try:
    with open("data.txt", "r") as f:
        content = f.read()
except FileNotFoundError:
    print("Error: File not found.")
except PermissionError:
    print("Error: Permission denied.")

# General error handling
try:
    # Your code here
    pass
except Exception as e:
    print(f"An error occurred: {e}")

Best Practice

Be specific with exception types. Catch ValueError or FileNotFoundError rather than generic Exception when possible.

Testing Your Code

Test your project thoroughly:

Test Normal Cases

Verify features work with expected input

Test Edge Cases

Try empty input, very long input, boundary values

Test Error Cases

Verify error handling works correctly

Fix Issues

Address any problems you find

Testing Example

def test_add_task():
    """Test adding a task."""
    tasks = []
    tasks = add_task(tasks, "Buy groceries")
    assert len(tasks) == 1
    assert tasks[0]["name"] == "Buy groceries"
    print("✓ Test passed!")

# Test edge cases
def test_empty_input():
    """Test handling empty input."""
    try:
        result = process_input("")
        assert False, "Should have raised an error"
    except ValueError:
        print("✓ Empty input handled correctly!")

Summary

In this lesson, you learned:

Error handling: Use try-except to handle errors gracefully
Testing: Test normal cases, edge cases, and error cases
Reliability: Make your project robust and professional
Best practices: Be specific with exceptions, test thoroughly

Remember

Error handling and testing are essential for professional projects. Take time to test thoroughly and handle errors gracefully. Your users will appreciate it!

End-of-Lesson Exercises

Think about these questions to reinforce what you've learned:

Exercise 1: Error Handling

Why is error handling important? How do you use try-except blocks?

Exercise 2: Testing

What should you test in your project? What are edge cases?

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