python実装ブロックチェーン

# !/usr/bin/env python
# -*- coding:utf-8 -*-
import hashlib as hasher
import datetime as date

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.hash_block(self)
    def hash_block(self):
        sha=hasher.sha256()
        sha.update(str(self.index)+str(self.timestamp)+str(self.data)+str(self.previous_hash))
        return sha.hexdigest()

#     
def create_genesis_block():
    return Block(0,date.datetime.now(),'Genesis Block','0')

def next_block(last_block):
    this_index=last_block.index+1
    this_timestamp=date.datetime.now()
    this_data='hey      '+str(this_index)
    this_hash=last_block.hash
    return Block(this_index,this_timestamp,this_data,this_hash)

#          
blockchain=[create_genesis_block()]
previous_block=blockchain[0]
num_of_block_to_add=50
for i in range(0,num_of_block_to_add):
    block_to_add=next_block(previous_block)
    blockchain.append(block_to_add)
    previous_block=block_to_add