Blockchain

The Blockchain Implementation

The blockchain functionality is provided by a single class, BlockChain, in the toychain.blockchain module. It is a simple list of blocks, each block in the chain consisting of a dictionnary with the following keys:

• the index at which it is located in the chain,
• a timestamp of when the block was added to the chain,
• the list of transactions recorded in the block,
• the proof of validity for itself,
• a previous_hash tag referencing the hash of the previous block in the chain, for immutability.

What's in the Blockchain?

The json payload for an example block with a single transaction would look like this:

block = {
    "index": 1,
    "timestamp": 1506057125.900785,
    "transactions": [
        {
            "sender": "8527147fe1f5426f9dd545de4b27ee00",
            "recipient": "a77f5cdfa2934df3954a5c7c7da5df1f",
            "amount": 5,
        }
    ],
    "proof": 324984774000,
    "previous_hash": "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
}

A block contains:

• the index at which it is located in the chain,
• the timestamp of the block's creation,
• the list of transactions written in this block,
• the proof of work for this block, calculated from the previous block's proof of work,
• the hash of the previous block in the chain (previous_hash).

Want to learn a bit about Blockchains?

If you want to dive a bit into how cryptocurrencies and blockchains work, I recommend you watch this excellent video by 3Blue1Brown.