10.2 Syntax logical and runtime errors

When writing and running Python code, you'll encounter different types of errors: syntax errors, logical errors, and runtime errors. Understanding these errors and knowing how to identify and fix them is crucial for debugging and developing robust programs.

10.2a Syntax errors

• What are syntax errors?

Syntax errors occur when the Python interpreter encounters code that doesn't conform to the language's grammar rules. These errors are detected at compile time, meaning before the program starts running.

Example 10.2.1 - Syntax errors

# Missing a closing parenthesis
print("Hello, World!"

# Using an undefined variable name
x = 10
print(y)

# Incorrect indentation
def my_function():
print("Hello")

• How to identify and fix syntax errors

  • Check the error message - Python will provide a traceback with information about where the syntax error occurred.
  • Review the problematic line - Look for common mistakes like missing colons, parentheses, or indentation issues.
  • Use a code editor - Many modern code editors highlight syntax errors as you type.

10.2b Logical errors

  - What are logical errors?

Logical errors occur when the program runs without crashing, but produces incorrect results. These errors arise from flaws in the program's logic, and they're often the hardest to detect because the program doesn't throw an error message.

Example 10.2.2 - Logical errors

# Incorrect calculation logic
def calculate_area(length, width):
    return length + width  # Should be length * width

# Flawed conditional logic
def is_even(number):
    if number % 2 == 1:
        return True  # Should return False
    return False

• How to identify and fix logical errors

  • Review the algorithm - Ensure the logic of your code aligns with the intended problem-solving approach.
  • Use print statements - Add print statements to check intermediate values and verify that your code behaves as expected.
  • Write tests - Create test cases with known outputs to validate the correctness of your functions.

10.2c Runtime errors

  - What are runtime errors?

Runtime errors occur while the program is running. These errors typically cause the program to crash or behave unexpectedly. They are also known as exceptions.

Example 10.2.3 - Runtime errors

# Division by zero
x = 10 / 0

# Accessing an undefined index in a list
my_list = [1, 2, 3]
print(my_list[5])

# Trying to open a non-existent file
with open("non_existent_file.txt", "r") as file:
    content = file.read()

• How to identify and fix runtime errors

  • Check the error message - Python provides a traceback with information about where the runtime error occurred and what caused it.
  • Use exception handling - Implement try-except blocks to handle potential errors gracefully.

Understanding and fixing syntax, logical, and runtime errors is crucial for writing robust Python programs. Syntax errors are caught by the interpreter, logical errors require careful review and testing, and runtime errors can be managed using exception handling. By identifying the type of error and applying the appropriate debugging techniques, you can effectively troubleshoot and correct issues in your code.

10.2d Solve syntax and/or logical and/or runtime errors in a given algorithm.

Let's consider an example algorithm with syntax, logical, and runtime errors, and demonstrate how to identify and solve them.

Exercise 10.2.1 - Function to calculate the average of a list of numbers with faulty code**.

Identify and solve the errors in the algorithm below:

_{Exercise 10.2.1 - Model Answer - Make sure to work out the exercise before checking the model answer.}