Layer 2 solutions overview in Blockchain / Solidity - Mini Project: Build & Apply

Layer 2 Solutions Overview

📖 Scenario: You are working with blockchain data and want to organize information about Layer 2 solutions. Layer 2 solutions help blockchains handle more transactions quickly and cheaply by working on top of the main blockchain.

🎯 Goal: You will create a dictionary of Layer 2 solutions with their types, set a filter type, extract solutions of that type using dictionary comprehension, and finally print the filtered solutions.

📋 What You'll Learn

Create a dictionary called layer2_solutions with exact entries for solutions and their types

Create a variable called filter_type with the exact string value to filter solutions

Use dictionary comprehension to create a new dictionary called filtered_solutions containing only solutions matching filter_type

Print the filtered_solutions dictionary

💡 Why This Matters

🌍 Real World

Layer 2 solutions are important in blockchain to improve speed and reduce costs. Organizing and filtering these solutions helps developers and users understand options available.

💼 Career

Understanding how to manage and filter data structures like dictionaries is essential for blockchain developers working with Layer 2 technologies and other blockchain data.

1

Create the Layer 2 solutions dictionary

Create a dictionary called layer2_solutions with these exact entries: 'Optimism': 'Optimistic Rollup', 'Arbitrum': 'Optimistic Rollup', 'Polygon': 'Sidechain', 'zkSync': 'ZK Rollup', 'Loopring': 'ZK Rollup'

Blockchain / Solidity

# Create the layer2_solutions dictionary with given entries
# Your code here

Hint

Use curly braces {} to create a dictionary with keys and values separated by colons.

2

Set the filter type

Create a variable called filter_type and set it to the string 'Optimistic Rollup'

Blockchain / Solidity

layer2_solutions = {
    'Optimism': 'Optimistic Rollup',
    'Arbitrum': 'Optimistic Rollup',
    'Polygon': 'Sidechain',
    'zkSync': 'ZK Rollup',
    'Loopring': 'ZK Rollup'
}
# Set filter_type to 'Optimistic Rollup'
# Your code here

Hint

Assign the string 'Optimistic Rollup' to the variable filter_type.

3

Filter solutions by type using dictionary comprehension

Use dictionary comprehension to create a new dictionary called filtered_solutions that contains only the entries from layer2_solutions where the value equals filter_type

Blockchain / Solidity

layer2_solutions = {
    'Optimism': 'Optimistic Rollup',
    'Arbitrum': 'Optimistic Rollup',
    'Polygon': 'Sidechain',
    'zkSync': 'ZK Rollup',
    'Loopring': 'ZK Rollup'
}
filter_type = 'Optimistic Rollup'
# Create filtered_solutions dictionary with comprehension
# Your code here

Hint

Use a dictionary comprehension with a condition to filter by filter_type.

4

Print the filtered solutions

Write a print statement to display the filtered_solutions dictionary

Blockchain / Solidity

layer2_solutions = {
    'Optimism': 'Optimistic Rollup',
    'Arbitrum': 'Optimistic Rollup',
    'Polygon': 'Sidechain',
    'zkSync': 'ZK Rollup',
    'Loopring': 'ZK Rollup'
}
filter_type = 'Optimistic Rollup'
filtered_solutions = {solution: typ for solution, typ in layer2_solutions.items() if typ == filter_type}
# Print the filtered_solutions dictionary
# Your code here

Hint

Use print(filtered_solutions) to show the filtered dictionary.

Practice

1. What is the main purpose of Layer 2 solutions in blockchain?

easy

A. To create new cryptocurrencies

B. To replace the main blockchain entirely

C. To store large files on the blockchain

D. To increase transaction speed and reduce costs by processing off the main chain

Solution

1. Step 1: Understand Layer 2 role

   Layer 2 solutions are designed to handle more transactions faster and cheaper by working off the main blockchain.

2. Step 2: Compare options

   Options A, B, and D describe unrelated blockchain functions, while C correctly states Layer 2's purpose.

3. Final Answer:

   To increase transaction speed and reduce costs by processing off the main chain -> Option D

4. Quick Check:

   Layer 2 purpose = Speed and cost efficiency [OK]

Hint: Layer 2 = faster, cheaper transactions off main chain [OK]

Common Mistakes:

• Thinking Layer 2 replaces the main blockchain
• Confusing Layer 2 with creating new coins
• Assuming Layer 2 stores large files

2. Which of the following is a correct example of a Layer 2 solution?

easy

A. State channels

B. Proof of Work consensus

C. Smart contracts on main chain

D. Mining pools

Solution

1. Step 1: Identify Layer 2 examples

   Common Layer 2 solutions include state channels, rollups, and sidechains.

2. Step 2: Match options to Layer 2

   State channels are Layer 2; Proof of Work and mining pools relate to Layer 1; smart contracts run on main chain, not Layer 2.

3. Final Answer:

   State channels -> Option A

4. Quick Check:

   Layer 2 example = State channels [OK]

Hint: State channels are classic Layer 2 solutions [OK]

Common Mistakes:

• Confusing consensus methods with Layer 2
• Thinking smart contracts are Layer 2
• Mixing mining pools with Layer 2

3. Consider this simplified code snippet representing a rollup process:

main_chain = []
rollup_batch = ["tx1", "tx2", "tx3"]
main_chain.append(rollup_batch)
print(len(main_chain[0]))

What will be the output?

medium

A. Error

B. 1

C. 3

D. 0

Solution

1. Step 1: Understand the code structure

   A list 'rollup_batch' with 3 transactions is appended as one item to 'main_chain'.

2. Step 2: Analyze the print statement

   main_chain[0] is the appended list ['tx1', 'tx2', 'tx3'], so its length is 3.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   Length of rollup batch = 3 [OK]

Hint: Appending list inside list keeps inner list length [OK]

Common Mistakes:

• Thinking length is 1 because one item appended
• Confusing length of outer list with inner list
• Expecting an error due to list append

4. This code tries to simulate a state channel update but has an error:

state_channel = {"balance": 100}
update = {"balance": 50}
state_channel.update(update)
print(state_channel["balance"])

What is the error and how to fix it?

medium

A. update() is not a method of dict, use state_channel = update

B. update() is a method but state_channel.update(update) modifies dict correctly, no error

C. update() is a method but should be called with parentheses as done, no fix needed

D. No error, output is 50

Solution

1. Step 1: Check dict update method usage

   Python dict has an update() method that merges another dict into it, called correctly here.

2. Step 2: Confirm output after update

   state_channel's 'balance' key is updated from 100 to 50, so print outputs 50 without error.

3. Final Answer:

   update() is a method but state_channel.update(update) modifies dict correctly, no error -> Option B

4. Quick Check:

   Dict update method works as expected [OK]

Hint: dict.update() merges keys, no error if used correctly [OK]

Common Mistakes:

• Thinking update() is not a dict method
• Confusing assignment with update method
• Expecting syntax error on update() call

5. You want to design a Layer 2 solution that bundles multiple transactions off-chain and submits a single proof to the main chain. Which Layer 2 type fits best and why?

hard

A. Rollups, because they bundle transactions and submit proofs to main chain

B. State channels, because they keep transactions private between participants

C. Sidechains, because they run a separate blockchain with their own consensus

D. Mining pools, because they combine mining power

Solution

1. Step 1: Understand Layer 2 types

   Sidechains run separate blockchains; state channels keep private off-chain transactions; rollups bundle transactions and submit proofs on-chain.

2. Step 2: Match requirement to Layer 2 type

   Bundling multiple transactions off-chain and submitting a single proof matches rollups' design.

3. Final Answer:

   Rollups, because they bundle transactions and submit proofs to main chain -> Option A

4. Quick Check:

   Bundling + proof submission = Rollups [OK]

Hint: Rollups bundle transactions and post proofs on main chain [OK]

Common Mistakes:

• Choosing sidechains which run separate chains
• Confusing state channels with bundling proofs
• Selecting mining pools unrelated to Layer 2