Assertion patterns in Blockchain / Solidity - Mini Project: Build & Apply

Assertion Patterns in Blockchain Smart Contracts

📖 Scenario: You are building a simple smart contract for a blockchain-based voting system. To ensure the contract works correctly, you will use assertion patterns to check important conditions during the voting process.

🎯 Goal: Create a smart contract that stores votes for candidates and uses assertions to verify that votes are valid and the voting process is correct.

📋 What You'll Learn

Create a dictionary to store candidates and their vote counts

Add a variable to track the minimum valid vote count

Use assertions to check that votes are only added to valid candidates and vote counts do not go below zero

Print the final vote counts

💡 Why This Matters

🌍 Real World

Assertions in smart contracts help catch errors early and prevent invalid transactions on the blockchain.

💼 Career

Blockchain developers use assertion patterns to write safer contracts that protect users and assets.

1

DATA SETUP: Create the initial vote counts

Create a dictionary called votes with these exact entries: 'Alice': 0, 'Bob': 0, 'Charlie': 0

Blockchain / Solidity

# Create a dictionary called votes with keys 'Alice', 'Bob', and 'Charlie' all set to 0
# Your code here

Need a hint?

Use curly braces to create a dictionary with the candidate names as keys and 0 as their initial vote counts.

2

CONFIGURATION: Set the minimum valid vote count

Create a variable called min_votes and set it to 0 to represent the minimum valid vote count

Blockchain / Solidity

votes = {'Alice': 0, 'Bob': 0, 'Charlie': 0}
# Create a variable min_votes and set it to 0
# Your code here

Need a hint?

This variable will help us check that votes never go below zero.

3

CORE LOGIC: Use assertions to validate votes

Write a for loop with variables candidate and count to iterate over votes.items(). Inside the loop, use assert to check that candidate is one of 'Alice', 'Bob', or 'Charlie', and that count is greater than or equal to min_votes

Blockchain / Solidity

votes = {'Alice': 0, 'Bob': 0, 'Charlie': 0}
min_votes = 0
# Use a for loop to iterate over votes.items() and assert candidate validity and count >= min_votes
# Your code here

Need a hint?

Assertions help us catch errors early by checking conditions that must always be true.

4

OUTPUT: Display the final vote counts

Write print(votes) to display the dictionary with the vote counts

Blockchain / Solidity

votes = {'Alice': 0, 'Bob': 0, 'Charlie': 0}
min_votes = 0
for candidate, count in votes.items():
    assert candidate in ['Alice', 'Bob', 'Charlie'], "Invalid candidate"
    assert count >= min_votes, "Vote count cannot be negative"
# Print the votes dictionary
# Your code here

Need a hint?

Printing the dictionary shows the current vote counts for each candidate.