2018-03-26
Blockchain implementation
Python implementation of blockchain in few lines of code.
In this blog post I'm sharing simple implementation of the blockchain idea - sequence of blocks protected and connected by using hashing algorithm.
Create data structure for block¶
block 'metadata':
- index - each block is numbered (has its index)
- timestamp - block creation time needed for conflict resolution
- previous hash -
signatureof previous block in chain - hash -
signatureof this block
data stored in block:
- data - actual 'payload' of the block
The hasher aggregate all elements of block (except this block hash) and calculates hash.
In [1]:
import hashlib as hasher
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()
def hash_block(self):
sha = hasher.sha256()
sha.update(
(
str(self.index)
+ str(self.timestamp)
+ str(self.data)
+ str(self.previous_hash)
).encode("utf-8")
)
return sha.hexdigest()
First block in chain is different from the rest in that sense that it has no predecessor - there is no previous block.
In [2]:
import datetime as date
def create_genesis_block():
# Manually construct a block with
# index zero and arbitrary previous hash
return Block(0, date.datetime.now(), "Genesis Block", "0")
Create next block based on last block
In [3]:
def next_block(last_block):
this_index = last_block.index + 1
this_timestamp = date.datetime.now()
this_data = "Hey! I'm block " + str(this_index)
this_hash = last_block.hash
return Block(this_index, this_timestamp, this_data, this_hash)
In [4]:
# Create the blockchain and add the genesis block
blockchain = [create_genesis_block()]
previous_block = blockchain[0]
# lenght of the blockchain (excluding genesis block)
num_of_blocks_to_add = 20
# Add blocks to the chain
for i in range(0, num_of_blocks_to_add):
block_to_add = next_block(previous_block)
blockchain.append(block_to_add)
previous_block = block_to_add
print("Block #{} has been added to the blockchain!".format(block_to_add.index))
print("Hash: {}\n".format(block_to_add.hash))
Out[8]: