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A demo of a naive blockchain data structure
# -*- 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()
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