A demo of a naive blockchain data structure

naive_blockchain.py

# -*- coding: utf-8 -*-

import json

from Crypto.Hash import SHA256
from datetime import datetime


class Block(object):
    """A class representing the block for the blockchain"""

    def __init__(self, index, previous_hash, timestamp, data, hash):
        self.index = index
        self.previous_hash = previous_hash
        self.timestamp = timestamp
        self.data = data
        self.hash = hash


class Blockchain(object):
    """A class representing list of blocks"""

    def __init__(self):

        self._chain = [self.get_genesis_block()]

    @property
    def chain(self):
        """created a dict containing list of block objects to view"""

        return self.dict(self._chain)

    def dict(self, chain):
        """converts list of block objects to dictionary"""

        return json.loads(json.dumps(chain, default=lambda o: o.__dict__))

    def reset(self):
        """resets the blockchain blocks except genesis block"""

        self._chain = [self._chain[0]]

    def get_genesis_block(self):
        """creates first block of the chain"""

        # SHA256.new(data=(str(0) + "0"+ str(1465154705) +"my genesis block!!").encode()).hexdigest()
        return Block(0, "0", 1465154705, "my genesis block!!",
                     "816534932c2b7154836da6afc367695e6337db8a921823784c14378abed4f7d7")

    def add_block(self, data):
        """appends a new block to the blockchain"""

        self._chain.append(self.create_block(data))


    def create_block(self, block_data):
        """creates a new block with the given block data"""

        previous_block = self.get_latest_block()
        next_index = previous_block.index + 1
        next_timestamp = int(datetime.now().timestamp())
        next_hash = self.calculate_hash(next_index, previous_block.hash, next_timestamp, block_data)
        return Block(next_index, previous_block.hash, next_timestamp, block_data, next_hash)

    def get_latest_block(self):
        """gets the last block from the blockchain"""

        try:
            return self._chain[-1]
        except IndexError as e:
            return None

    def calculate_hash(self, index, previous_hash, timestamp, data):
        """calculates SHA256 hash value"""

        hash_object = SHA256.new(data=(str(index) + previous_hash + str(timestamp) + data).encode())
        return hash_object.hexdigest()