Import the BlockChain class

from modstore.datastructures import BlockChain

Create a blockchain

To create a blockchain, we have to provide two parameters: difficulty (int) and timezone (for timestamps). The timezone parameter takes either ‘UTC’ and ‘IST’ string literals or a pattern in the form ‘HH:MM:SS’ defining the hours, minutes and seconds to be added to UTC time to get your required timezone.

blockchain = BlockChain(difficulty=10, timezone='IST')

At this point, the blockchain is ready with a genesis block as a placeholder for all other blocks to connect to. The genesis block does not have any content in it.

Add a block in the blockchain

For adding a block, we need two parameters: uniqueIdentifier (str) which uniquely identifies the block and data which can be any python object or string or bytes.

Internally, unless the data is string or bytes, all objects will be forcefully converted to bytes using pickle module.

# the data being used is a list of integers (object)
blockchain.addBlock(uniqueIdentifier='block-1', data=[1, 2, 3, 4])

Search for a block using its identifier and get the concerned block

Note that if the block is found, it will be returned as Block type. This is an internal type to represent a block within the blockchain and its sole purpose is to act as a return type for search method. Outside this, Block class object cannot exist.

# we will use the identifier we set during adding a block
first_block = blockchain.search(identifier='block-1')

This first_block variable is of the type Block and has a few properties that can be used to get information about this block.

# index of the block
index = first_block.index

# timestamp of creation
timestamp = first_block.timestamp

# identifier of the block
identifier = first_block.identifier

# previous block's hash (in this case the previous block is the genesis block)
previous_hash = first_block.previous_hash

# hash of the block
_hash = first_block.hash

# the contents of the block
contents = first_block.data()
# Note that this will return the value in bytes if the original data given
# was an object or bytes and str if the original data was str.

# to get the original data as it is
contents = first_block.data(return_original=True) # [1, 2, 3, 4] as we added.

Get a list of identifiers of blocks that are currently in the blockchain

identifiers = blockchain.identifiers() # returns ['block-1'] as of now..

Validity of the blockchain and length

Validity means tamper free and consistent according to the difficulty factor set.

if blockchain.valid:
    print('blockchain is valid')
else:
    print('someone tampered with the internal mechanism.')
    print('current blockchain length:', blockchain.length)

Printing the blockchain

print(blockchain)

# or in the python shell:
>>> blockchain