blockchain.simple_blockchain

A simple blockchain implementation with Proof-of-Work (PoW).

This educational example demonstrates: - Block structure with index, timestamp, data, previous hash, nonce, and hash - Mining via Proof-of-Work - Chain integrity verification

Author: Letitia Gilbert

Classes

Block	Represents a single block in a blockchain.
Blockchain	Simple blockchain class maintaining a list of blocks.

Module Contents

class blockchain.simple_blockchain.Block(index: int, data: str, previous_hash: str, difficulty: int = 2)

Represents a single block in a blockchain.

Attributes:

index (int): Position of the block in the chain. timestamp (float): Creation time of the block. data (str): Data stored in the block. previous_hash (str): Hash of the previous block. nonce (int): Number used for mining. hash (str): SHA256 hash of the block’s content.

compute_hash(nonce: int) → str

Compute SHA256 hash of the block with given nonce.

Args:

nonce (int): Nonce to include in the hash.

Returns:

str: Hexadecimal hash string.

>>> block = Block(0, "Genesis", "0", difficulty=2)
>>> len(block.compute_hash(0)) == 64
True
>>> isinstance(block.compute_hash(0), str)
True

mine_block(difficulty: int) → tuple[int, str]

Simple Proof-of-Work mining algorithm.

Args:

difficulty (int): Number of leading zeros required in the hash.

Returns:

Tuple[int, str]: Valid nonce and resulting hash that satisfies difficulty.

>>> block = Block(0, "Genesis", "0", difficulty=2)
>>> block.hash.startswith('00')
True

data

index

previous_hash

timestamp

class blockchain.simple_blockchain.Blockchain(difficulty: int = 2)

Simple blockchain class maintaining a list of blocks.

Attributes:

chain (List[Block]): List of blocks forming the chain.

add_block(data: str) → Block

Add a new block to the blockchain with given data.

Args:

data (str): Data to store in the block.

Returns:

Block: Newly added block.

>>> bc = Blockchain()
>>> new_block = bc.add_block("Test Data")
>>> new_block.index
1
>>> new_block.previous_hash == bc.chain[0].hash
True
>>> new_block.hash.startswith('00')
True
>>> bc.is_valid()
True

create_genesis_block() → Block

Create the first block in the blockchain.

Returns:

Block: Genesis block.

>>> bc = Blockchain()
>>> bc.chain[0].index
0
>>> bc.chain[0].hash.startswith('00')
True

is_valid() → bool

Verify the integrity of the blockchain.

Returns:

bool: True if chain is valid, False otherwise.

>>> bc = Blockchain()
>>> new_block = bc.add_block("Test")
>>> new_block.index
1
>>> new_block.previous_hash == bc.chain[0].hash
True
>>> new_block.hash.startswith('00')
True
>>> bc.is_valid()
True
>>> bc.chain[1].previous_hash = "tampered"
>>> bc.is_valid()
False

chain: list[Block]

difficulty = 2