blockchain.py

from collections import namedtuple
from hashlib import sha256
from typing import List, Optional


def makehash(data: str) -> str:
    return sha256(data.encode()).hexdigest()


Block = namedtuple("Block", ["data", "hash", "prevhash"])


class BlockChain:
    def __init__(self):
        self.blocks = []  # type: List[Block]

    def add_block(self, data: str):
        prevblock = self.blocks[-1] if self.blocks else None  # type: Block
        prevhash = "" if prevblock is None else prevblock.hash
        newblock = Block(data, makehash(prevhash + makehash(data)), prevhash)
        self.blocks.append(newblock)


if __name__ == "__main__":
    data = ["My hovercraft is full of eels", "Frobnicating in chains", 
            "Dick Laurent is dead", "Rosebud"]
    chain = BlockChain()
    for i, item in enumerate(data):
        chain.add_block(item)
        print("block #%d: %s" % (i + 1, chain.blocks[i].hash))