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class Block:
    def __init__(self, index, transactions, timestamp, previous_hash, nonce = 0):
        self.index = index
        self.transactions = transactions # data
        self.timestamp = timestamp
        self.previous_hash = previous_hash
        self.nonce = nonce

    def compute_hash(self):
        block_string = json.dumps(self.__dict__, sort_keys=True)

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class Blockchain:
    # difficulty of our PoW algorithm
    difficulty = 2

    def __init__(self):
        self.unconfirmed_transactions = []
        self.chain = []  #store chain of Block  

    @property
    def last_block(self):

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class Blockchain:
    """
        previous code...
    """
    def proof_of_work(self, block):
        """
        Function that tries different values of nonce to get a hash
        that satisfies our difficulty criteria.
        """
        block.nonce = 0

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class Block:
    """
        previous code...
    """
    def add_block(self, block, proof):
        """
        A function that adds the block to the chain after verification.
        Verification includes:
        * Checking if the proof is valid.
        * The previous_hash referred in the block and the hash of latest block

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from flask import Flask, request
import requests

# Initialize flask application
app =  Flask(__name__)

# Initialize a blockchain object.
blockchain = Blockchain()

# Flask's way of declaring end-points

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def consensus():
    """
    Our simple consensus algorithm. If a longer valid chain is
    found, our chain is replaced with it.
    """
    global blockchain

    longest_chain = None
    current_len = len(blockchain.chain)