Distributed ledger concept in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a new block to the blockchain list.

Blockchain / Solidity

blockchain.append([1])

Drag options to blanks, or click blank then click option'

A['index', 1, 'data', 'Genesis Block']

B'Genesis Block'

C{'index': 1, 'data': 'Genesis Block'}

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Appending a string or list instead of a dictionary.

Appending just a number.

The blockchain stores blocks as dictionaries with keys like 'index' and 'data'. So we append a dictionary representing the new block.

2fill in blank

medium

Complete the code to calculate the hash of a block's data string.

Blockchain / Solidity

block_hash = hashlib.sha256([1].encode()).hexdigest()

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Ablock['timestamp']

Bblock['previous_hash']

Cblock['index']

Dblock['data']

Attempts:

3 left

💡 Hint

Common Mistakes

Hashing the index or timestamp instead of data.

The hash is usually calculated from the block's data content to ensure integrity.

3fill in blank

hard

Fix the error in the code to verify if the blockchain is valid by checking hashes.

Blockchain / Solidity

if blockchain[i]['previous_hash'] != blockchain[[1]]['hash']:
    return False

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Ai-1

Blen(blockchain)

C0

Di+1

Attempts:

3 left

💡 Hint

Common Mistakes

Using i+1 which is the next block, not previous.

Using 0 which always points to the first block.

Each block's previous_hash should match the hash of the block before it, which is at index i-1.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps block indices to their data if the data length is greater than 5.

Blockchain / Solidity

{block['index']: block[1] for block in blockchain if len(block[2]) > 5}

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A['data']

B['index']

D['hash']

Attempts:

3 left

💡 Hint

Common Mistakes

Using ['index'] as value instead of ['data'].

Checking length of wrong field.

The comprehension maps block indices to their data. We access 'data' for the value and check its length.

5fill in blank

hard

Fill all three blanks to create a dictionary of block hashes to their data for blocks with index greater than 0.

Blockchain / Solidity

{block[1]: block[2] for block in blockchain if block[3] > 0}

Drag options to blanks, or click blank then click option'

A['hash']

B['data']

C['index']

D['previous_hash']

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong keys or values.

Filtering on wrong field.

The dictionary uses block hashes as keys and data as values, filtering blocks with index > 0.