Linked List implementation of a simple blockchain

blockchain_linkedlist.py

# blockchain implementation using Linked List
# Copyright: Renee S. Liu

# First is the information hash
# We do this for the information we want to store in the block chain
# such as transaction time, data, and information like the previous chain.
import hashlib
import datetime as date

# The next main component is the block class
class Block:

    def __init__(self, index, timestamp, data, previous_hash):
        self.index = index
        self.timestamp = timestamp
        self.data = data
        self.previous_hash = previous_hash
        self.hash = self.calc_hash()
        self.prev = None
    
        
    def calc_hash(self):
        sha = hashlib.sha256()
        sha.update(str(self.index).encode('utf-8') +
                   str(self.timestamp).encode('utf-8') + 
                   str(self.data).encode('utf-8') +
                   str(self.previous_hash).encode('utf-8'))

        return sha.hexdigest()

# This creates a first block in a chain  
def create_block_eve():
    """
    create genesis block - eve
    Initialize with arbitrary data and previous_hash values
    """   
    return Block(0, date.datetime.now(), 'heijre', 'uroe46jkf')


def createNewblock(Prevblock):
    new_index = Prevblock.index + 1
    new_timestamp = date.datetime.now()
    new_data = "Block {} was created at ".format(new_index) + new_timestamp.strftime('%m/%d/%y:%H:%M:%S:%f-%Z')
    new_previous_hash = Prevblock.hash
    new_prev = Prevblock
    return Block(new_index, new_timestamp, new_data, new_previous_hash)

block_1 = createNewblock(genesis_block)


# Implementing Blockchain structure with a Linked List under the hood
class BlockChain_ll:
    
    def __init__(self):
        first_tail = create_block_eve()
        self.head = first_tail
        self.tail = first_tail
        self.num_new_blocks = 0
        

    
    def append(self, new_block):
        if self.tail == None:
            print("Create genesis first!")
            self.tail = genesis_block
        else:
            temp_block = self.tail
            self.tail = new_block
            self.tail.prev = temp_block
            self.num_new_blocks += 1
            del temp_block

            
    def size(self):
        
        return self.num_new_blocks + 1


   def get_block(self, index):
        
        tail_block = self.tail
        tail_idx = tail_block.index
        temp_tail_block = tail_block
        
        if tail_idx == index:
            return tail_block
        
        if tail_idx < index:
            return "Block index invalid"
            
        while tail_idx > index:
            temp_tail_block = temp_tail_block.prev
            tail_idx = temp_tail_block.index
            
        return temp_tail_block 

#########################################

# create 20 blocks        

# Initialize the blockchain
# get the genesis block from it
blockchain = BlockChain_ll()
gene_block = blockchain.tail
blockchain = BlockChain_ll()
gene_block = blockchain.tail
old_block = gene_block

for i in range(20):
    new_block = createNewblock(old_block)
    blockchain.append(new_block)
    old_block = new_block
  
  


########################## Test ###############
# Blockchain
blockchain.get_block(20).index
blockchain.get_block(15).index
blockchain.get_block(15).data
print(blockchain.tail.index)
blockchain.append(block_1)
print(blockchain.tail.index)
blockchain.append(block_2)
print(blockchain.tail.index)
blockchain.append(block_3)
print(blockchain.tail.index)
blockchain.size()


# check the tail index
blockchain.tail.index

# check the index of the block before the tail
blockchain.tail.prev.index