A blockchain made from scratch in ~50 lines

blockchain.py

# source: https://twitter.com/PrasoonPratham/status/1461267623266635778/photo/1 (@PrasoonPratham on Twitter)
import datetime
import hashlib

class Block:
    def __init__(self, data):
        self.data = data
        self.blockNo = 0
        self.next = None
        self.nonce = 0
        self.previous_hash = 0x0
        self.timestamp = datetime.datetime.now()
    # get block hash
    def hash(self):
        h = hashlib.sha256()
        h.update(
            str(self.nonce).encode('utf-8') +
            str(self.data).encode('utf-8') +
            str(self.previous_hash).encode('utf-8') +
            str(self.timestamp).encode('utf-8') +
            str(self.blockNo).encode('utf-8')
        )
        return h.hexdigest()
    def __str__(self):
        return "Block Hash: " + str(self.hash()) + "\nBlockNo: "  + str(self.blockNo) + "\nBlock Data: " + str(self.data) + "\nHashes:" + str(self.nonce) +"\n--------------"

class Blockchain:
    def __init__(self):
        self.diff = 20
        self.maxNonce = 2**32
        self.target = 2 ** (256-self.diff)
        self.block = Block("Genesis")
        self.dummy = self.head = self.block
    # add a block
    def add(self, block):
        block.previous_hash = self.block.hash()
        block.blockNo = self.block.blockNo + 1
        self.block.next = block
        self.block = self.block.next
    # mine a block
    def mine(self, block):
        for _ in range (self.maxNonce):
            if int(block.hash(), 16) <= self.target:
                self.add(block)
                print(block)
                break
            else:
                block.nonce += 1
# create a blockchain
blockchain = Blockchain()
# mine 16 blocks
for n in range (16):
    blockchain.mine(Block("Block " + str(n+1)))
# print the blockchain
while blockchain.head != None:
    print(blockchain.head)
    blockchain.head = blockchain.head.next