class Block:

 def __init__():

 #first block class

  pass
 
 def calculate_hash():
 
 #calculates the cryptographic hash of every block
  
 
class BlockChain:
 
 def __init__(self):
  # constructor method
 pass
 
 def construct_genesis(self):
  # constructs the initial block
  pass

 def construct_block(self, proof_no, prev_hash):
  # constructs a new block and adds it to the chain
  pass

 @staticmethod
 def check_validity():
  # checks whether the blockchain is valid
  pass

 def new_data(self, sender, recipient, quantity):
  # adds a new transaction to the data of the transactions
  pass

 @staticmethod
 def construct_proof_of_work(prev_proof):
  # protects the blockchain from attack
  pass
 
 @property
 def last_block(self):
  # returns the last block in the chain
  return self.chain[-1]

import hashlib
import time

class Block:

 def __init__(self, index, proof_no, prev_hash, data, timestamp=None):
  self.index = index
  self.proof_no = proof_no
  self.prev_hash = prev_hash
  self.data = data
  self.timestamp = timestamp or time.time()

 @property
 def calculate_hash(self):
  block_of_string = "{}{}{}{}{}".format(self.index, self.proof_no,
            self.prev_hash, self.data,
            self.timestamp)

  return hashlib.sha256(block_of_string.encode()).hexdigest()

 def __repr__(self):
  return "{} - {} - {} - {} - {}".format(self.index, self.proof_no,
            self.prev_hash, self.data,
            self.timestamp)

{
 "index": 2,
 "proof": 21,
 "prev_hash": "6e27587e8a27d6fe376d4fd9b4edc96c8890346579e5cbf558252b24a8257823",
 "transactions": [
  {'sender': '0', 'recipient': 'Quincy Larson', 'quantity': 1}
 ],
 "timestamp": 1521646442.4096143
}

class BlockChain:

 def __init__(self):
  self.chain = []
  self.current_data = []
  self.nodes = set()
        self.construct_genesis()

def construct_genesis(self):
 self.construct_block(proof_no=0, prev_hash=0)


def construct_block(self, proof_no, prev_hash):
 block = Block(
  index=len(self.chain),
  proof_no=proof_no,
  prev_hash=prev_hash,
  data=self.current_data)
 self.current_data = []

 self.chain.append(block)
 return block

@staticmethod
def check_validity(block, prev_block):
 if prev_block.index + 1 != block.index:
  return False

 elif prev_block.calculate_hash != block.prev_hash:
  return False

 elif not BlockChain.verifying_proof(block.proof_no, prev_block.proof_no):
  return False

 elif block.timestamp <= prev_block.timestamp:
  return False

 return True

def new_data(self, sender, recipient, quantity):
 self.current_data.append({
  'sender': sender,
  'recipient': recipient,
  'quantity': quantity
 })
 return True

@staticmethod
def proof_of_work(last_proof):
 '''this simple algorithm identifies a number f' such that hash(ff') contain 4 leading zeroes
   f is the previous f'
   f' is the new proof
  '''
 proof_no = 0
 while BlockChain.verifying_proof(proof_no, last_proof) is False:
  proof_no += 1

 return proof_no


@staticmethod
def verifying_proof(last_proof, proof):
 #verifying the proof: does hash(last_proof, proof) contain 4 leading zeroes?

 guess = f'{last_proof}{proof}'.encode()
 guess_hash = hashlib.sha256(guess).hexdigest()
 return guess_hash[:4] == "0000"

@property
 def latest_block(self):
  return self.chain[-1]

import hashlib
import time


class Block:

 def __init__(self, index, proof_no, prev_hash, data, timestamp=None):
  self.index = index
  self.proof_no = proof_no
  self.prev_hash = prev_hash
  self.data = data
  self.timestamp = timestamp or time.time()

 @property
 def calculate_hash(self):
  block_of_string = "{}{}{}{}{}".format(self.index, self.proof_no,
            self.prev_hash, self.data,
            self.timestamp)

  return hashlib.sha256(block_of_string.encode()).hexdigest()

 def __repr__(self):
  return "{} - {} - {} - {} - {}".format(self.index, self.proof_no,
            self.prev_hash, self.data,
            self.timestamp)


class BlockChain:

 def __init__(self):
  self.chain = []
  self.current_data = []
  self.nodes = set()
  self.construct_genesis()

 def construct_genesis(self):
  self.construct_block(proof_no=0, prev_hash=0)

 def construct_block(self, proof_no, prev_hash):
  block = Block(
   index=len(self.chain),
   proof_no=proof_no,
   prev_hash=prev_hash,
   data=self.current_data)
  self.current_data = []

  self.chain.append(block)
  return block

 @staticmethod
 def check_validity(block, prev_block):
  if prev_block.index + 1 != block.index:
   return False

  elif prev_block.calculate_hash != block.prev_hash:
   return False

  elif not BlockChain.verifying_proof(block.proof_no,
           prev_block.proof_no):
   return False

  elif block.timestamp <= prev_block.timestamp:
   return False

  return True

 def new_data(self, sender, recipient, quantity):
  self.current_data.append({
   'sender': sender,
   'recipient': recipient,
   'quantity': quantity
  })
  return True

 @staticmethod
 def proof_of_work(last_proof):
  '''this simple algorithm identifies a number f' such that hash(ff') contain 4 leading zeroes
   f is the previous f'
   f' is the new proof
  '''
  proof_no = 0
  while BlockChain.verifying_proof(proof_no, last_proof) is False:
   proof_no += 1

  return proof_no

 @staticmethod
 def verifying_proof(last_proof, proof):
  #verifying the proof: does hash(last_proof, proof) contain 4 leading zeroes?

  guess = f'{last_proof}{proof}'.encode()
  guess_hash = hashlib.sha256(guess).hexdigest()
  return guess_hash[:4] == "0000"

 @property
 def latest_block(self):
  return self.chain[-1]

 def block_mining(self, details_miner):

  self.new_data(
   sender="0", #it implies that this node has created a new block
   receiver=details_miner,
   quantity=
   1, #creating a new block (or identifying the proof number) is awarded with 1
  )

  last_block = self.latest_block

  last_proof_no = last_block.proof_no
  proof_no = self.proof_of_work(last_proof_no)

  last_hash = last_block.calculate_hash
  block = self.construct_block(proof_no, last_hash)

  return vars(block)

 def create_node(self, address):
  self.nodes.add(address)
  return True

 @staticmethod
 def obtain_block_object(block_data):
  #obtains block object from the block data

  return Block(
   block_data['index'],
   block_data['proof_no'],
   block_data['prev_hash'],
   block_data['data'],
   timestamp=block_data['timestamp'])

blockchain = BlockChain()

print("***Mining fccCoin about to start***")
print(blockchain.chain)

last_block = blockchain.latest_block
last_proof_no = last_block.proof_no
proof_no = blockchain.proof_of_work(last_proof_no)

blockchain.new_data(
 sender="0", #it implies that this node has created a new block
 recipient="Quincy Larson", #let's send Quincy some coins!
 quantity=
 1, #creating a new block (or identifying the proof number) is awarded with 1
)

last_hash = last_block.calculate_hash
block = blockchain.construct_block(proof_no, last_hash)

print("***Mining fccCoin has been successful***")
print(blockchain.chain)

***Mining fccCoin about to start***
[0 - 0 - 0 - [] - 1566930640.2707076]
***Mining fccCoin has been successful***
[0 - 0 - 0 - [] - 1566930640.2707076, 1 - 88914 - a8d45cb77cddeac750a9439d629f394da442672e56edfe05827b5e41f4ba0138 - [{'sender': '0', 'recipient': 'Quincy Larson', 'quantity': 1}] - 1566930640.5363243]