Let’s Build the Tiniest Blockchain in Python 3.

snakecoin.py

import hashlib as hasher
import datetime as date


# Define what a Snakecoin block is
class Block:
    def __init__(self, index, timestamp, data, previous_hash):
        self.index = index
        self.timestamp = timestamp
        self.data = data
        self.previous_hash = previous_hash
        self.hash = self.hash_block()

    def hash_block(self):
        sha = hasher.sha256()
        sha.update(str(self.index).encode('utf-8') +
                   str(self.timestamp).encode('utf-8') +
                   str(self.data).encode('utf-8') +
                   str(self.previous_hash).encode('utf-8'))
        return sha.hexdigest()


# Generate genesis block
def create_genesis_block():
    # Manually construct a block with
    # index zero and arbitrary previous hash
    return Block(0, date.datetime.now(), "Genesis Block", "0")


# Generate all later blocks in the blockchain
def next_block(last_block):
    this_index = last_block.index + 1
    this_timestamp = date.datetime.now()
    this_data = "Hey! I'm block " + str(this_index)
    this_hash = last_block.hash
    return Block(this_index, this_timestamp, this_data, this_hash)


# Add blocks to the chain
def add_block(blockchain, previous_block):
    block_to_add = next_block(previous_block)
    blockchain.append(block_to_add)
    previous_block = block_to_add
    # Tell everyone about it!
    print("Block #{} has been added to the blockchain!"
          .format(block_to_add.index))
    print("Hash: {}\n".format(block_to_add.hash))


def main():
    # Create the blockchain and add the genesis block
    blockchain = [create_genesis_block()]
    previous_block = blockchain[0]
    # How many blocks should we add to the chain
    # after the genesis block
    num_of_blocks_to_add = 20
    # Build the blockchain with a list comprehension
    [add_block(blockchain, previous_block)
     for i in range(num_of_blocks_to_add)]

if __name__ == '__main__':
    main()