Debugging Code

• Computing
• Upper Secondary (Key Stage 4)
• GCSE

Debugging and Tracing Code

Year 10

KO: To identify common mistakes when programming in Python

All

To identify the common 'mistakes' made when programming in Python.

Most 

To identify the common 'mistakes' when programming in Python and fix them.

Some 

To be-able to use a trace table, when debugging code in Python.

What is Debugging? What is it's purpose?

What do you think the most common mistakes in programming are?

Syntax Errors

These are errors that occur when you violate the rules of the Python language. For example, forgetting to include a colon at the end of an if statement, or not properly indenting the code within a loop or function. The compiler will not run with a Syntax error.

Debugging Code - Syntax Errors

First Task

Second Task 

Third Task

First Task - Corrected Code

for i in range(10):

    print(i)

Second Task - Corrected Code

password = input("Please enter your password:")

if password == "Password123":

  print("Password is correct")

else:

  print("Password is not correct")

Third Task - Corrected Code

count = 0

while count < 5:

    print("Count is:", count)

    count = count + 1

print("Loop finished")

Name Errors

These errors occur when you reference a variable or function that has not been defined or assigned a value.

Debugging Code - Name Errors 

First Task

Second Task

Third Task

First Task - Corrected Code

x = 42

print(x)

Second Task - Corrected Code

my_variable = "Hello, world!"

print(my_variable)

Third Task - Corrected Code

fruits = ['apple', 'banana', 'orange']

print(fruits[1])

Type Errors

These occur when you try to perform operations on incompatible data types, such as trying to add an integer and a string.

Debugging Code - Type Errors

First Task

Second Task

Third Task

First Task - Corrected Code

x = "42"

y = 2

print(int(x) + y)

Second Task - Corrected Code

food = "bar"

print(food)

Third Task - Corrected Code

num1 = "10"

num2 = 5

sum = int(num1) + num2

print(sum)

Logical Errors

These occur when your code does not produce the expected output due to incorrect algorithms or decision-making. A program with a logical error can still compile and run without any syntax errors, but the program will not produce the intended output or behaviour.

Debugging Code - Logical Errors

First Task

Second Task

Third Task

First Task - Corrected Code

x = (2 + 3) * 4 # addition needs to be performed first

print(x)

Second Task - Corrected Code

age = int(input("How old are you?"))

if age >= 18:

    print("You are an adult")

    

else:

  print("You are not an adult")

Third Task - Corrected Code

x = 10

while x > 0:

    print(x)

    x = x + 1

Casting (Data Type Conversion)

Casting in programming refers to the process of converting one data type to another. It is also known as type conversion.

Logical 

Syntax

Infinite loops

Uninitialised variables

Misspelled keywords

Missing or extra punctuation

Incorrect data types

Incorrect function or method calls

Division by zero

What do you think a 'Trace Table is'?

What is a Trace Table?

• A trace table is a tool used in computer programming to trace and visualise the execution of a program. It is a table that shows the values of variables at different stages of the program's execution. 

• The trace table is used to keep track of the program's control flow and the values of the variables as the program executes line by line.

What does a Trace Table look like?

• In a trace table, the columns represent the variables used in the program, and the rows represent the stages of the program's execution. Each cell in the table represents the value of a variable at a particular stage of the program's execution.

Example

Tracing Table Tasks

Task 1 - Click here

Task 2 - Click here

Task 3 - Click here

Task 4 - Click here

Fix this code!

Click here

Think about what we have looked at today!

Solution

def find_average(numbers):

    total = 0

    for num in numbers:

        total += num

    avg = total / len(numbers)

    return avg

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

average = find_average(numbers)

print("The average is: " + str(average))

What are the benefits of using a Trace Table?

1. Makes code run faster
2. Makes code harder to read
3. Helps identify errors and improve code understanding
4. Allows for easier code duplication

What is a type error in Python?

1. When the code is not indented correctly.
2. When a variable is not defined.
3. When an operation or function is applied to an object of inappropriate type.
4. When there is a syntax error.