Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat.

–– coding: utf-8 ––

from hashlib import sha256
import json
from time import time

class Block:

def __init__(self, timestamp=None, data=None):
    self.timestamp = timestamp or time()
    self.data = [] if data is None else data
    self.prevHash = None
    self.nonce = 0
    self.hash = self.getHash()

def getHash(self):

    hash = sha256()
    hash.update(str(self.prevHash).encode('utf-8'))
    hash.update(str(self.timestamp).encode('utf-8'))
    hash.update(str(self.data).encode('utf-8'))
    hash.update(str(self.nonce).encode('utf-8'))
    return hash.hexdigest()

def mine(self, difficulty):
    while self.hash[:difficulty] != '0' * difficulty:
        self.nonce += 1
        self.hash = self.getHash()

class Blockchain:

def __init__(self):
    self.chain = [Block(str(int(time())))]
    self.difficulty = 1
    self.blockTime = 30000

def getLastBlock(self):
    return self.chain[len(self.chain) - 1]

def addBlock(self, block):
    block.prevHash = self.getLastBlock().hash
    block.hash = block.getHash()
    block.mine(self.difficulty)
    self.chain.append(block)

    self.difficulty += (-1, 1)[int(time()) - int(self.getLastBlock().timestamp) < self.blockTime]

def isValid(self):
    for i in range(1, len(self.chain)):
        currentBlock = self.chain[i]
        prevBlock = self.chain[i - 1]

        if (currentBlock.hash != currentBlock.getHash() or prevBlock.hash != currentBlock.prevHash):
            return False

    return True

def __repr__(self):
    return json.dumps([{'data': item.data, 'timestamp': item.timestamp, 'nonce': item.nonce, 'hash': item.hash, 'prevHash': item.prevHash} for item in self.chain], indent=4)