State diagrams in Software Engineering - Mini Project: Build & Apply

Understanding State Diagrams

📖 Scenario: You are designing a simple state diagram for a traffic light system. The traffic light can be in one of three states: Red, Green, or Yellow. It changes states in a fixed order to control traffic flow safely.

🎯 Goal: Create a step-by-step representation of the traffic light's state diagram using a dictionary in Python. Each state will have the next state it transitions to. This will help you understand how state diagrams map real-world processes.

📋 What You'll Learn

Create a dictionary named traffic_light_states with keys as state names and values as the next state.

Add a variable named initial_state set to 'Red'.

Write a loop that iterates through the states starting from initial_state and collects the sequence of states.

Add a final step to show the complete sequence of states in order.

💡 Why This Matters

🌍 Real World

State diagrams help model systems like traffic lights, vending machines, or user interfaces to understand how they change over time.

💼 Career

Understanding state diagrams is important for software engineers, system designers, and testers to design reliable and predictable systems.

1

Create the initial state dictionary

Create a dictionary called traffic_light_states with these exact entries: 'Red': 'Green', 'Green': 'Yellow', and 'Yellow': 'Red'.

Software Engineering

# Create the traffic_light_states dictionary
# Your code here

Hint

Think of each state as a key, and the next state as its value.

2

Set the initial state

Add a variable called initial_state and set it to the string 'Red'.

Software Engineering

traffic_light_states = {'Red': 'Green', 'Green': 'Yellow', 'Yellow': 'Red'}
# Set the initial state
# Your code here

Hint

The initial state is where the traffic light starts.

3

Create a loop to follow the state transitions

Write a for loop that starts from initial_state and iterates 4 times, each time updating the current state to the next state from traffic_light_states. Store each visited state in a list called state_sequence.

Software Engineering

traffic_light_states = {'Red': 'Green', 'Green': 'Yellow', 'Yellow': 'Red'}
initial_state = 'Red'

# Create a list to store the sequence
# Your code here

Hint

Use a list to keep track of states and update the current state each loop.

4

Complete the state sequence representation

Add a final line that assigns the list state_sequence to a variable called final_sequence to represent the full cycle of states.

Software Engineering

traffic_light_states = {'Red': 'Green', 'Green': 'Yellow', 'Yellow': 'Red'}
initial_state = 'Red'

state_sequence = []
current_state = initial_state
for _ in range(4):
    state_sequence.append(current_state)
    current_state = traffic_light_states[current_state]

# Assign the final sequence
# Your code here

Hint

This final variable holds the full order of states visited.