A simple tutorial for developing a blockchain application from scratch in Python.

Please read the step-by-step implementation tutorial to get your answers :)

Clone the project,

$ git clone https://github.com/satwikkansal/python_blockchain_app.git

Install the dependencies,

$ cd python_blockchain_app
$ pip install -r requirements.txt

Start a blockchain node server,

# Windows users can follow this: https://flask.palletsprojects.com/en/1.1.x/cli/#application-discovery
$ export FLASK_APP=node_server.py
$ export FLASK_ENV=development
$ python -m flask run --port 8000

One instance of our blockchain node is now up and running at port 8000.

Run the application on a different terminal session,

$ python run_app.py

If you run the code on port 9000, you will have a client generating txs:

python node_server.py --port 9000

The application should be up and running at http://localhost:5000.

Here are a few screenshots

1. Posting some content

2. Requesting the node to mine

3. Resyncing with the chain for updated data

To play around by spinning off multiple custom nodes, use the register_with/ endpoint to register a new node.

Here's a sample scenario that you might wanna try,

# Make sure you set the FLASK_APP environment variable to node_server.py before running these nodes
# already running
$ flask run --port 8000 &
# spinning up new nodes
$ flask run --port 8001 &
$ flask run --port 8002 &

You can use the following cURL requests to register the nodes at port 8001 and 8002 with the already running 8000.

curl -X POST \
  http://127.0.0.1:8001/register_with \
  -H 'Content-Type: application/json' \
  -d '{"node_address": "http://127.0.0.1:8000", "req_chain": 1}'

curl -X POST \
  http://127.0.0.1:8002/register_with \
  -H 'Content-Type: application/json' \
  -d '{"node_address": "http://127.0.0.1:8000", "req_chain": 0}'

This will make the node at port 8000 aware of the nodes at port 8001 and 8002, and makes the node at port 8001 sync the chain with the node 8000, so that it is able to actively participate in the mining process post registration.

To update the node with which the frontend application syncs (default is localhost port 8000), change CONNECTED_NODE_ADDRESS field in the views.py file.

Once you do all this, you can run the application, create transactions (post messages via the web inteface), and once you mine the transactions, all the nodes in the network will update the chain. The chain of the nodes can also be inspected by inovking /chain endpoint using cURL.

$ curl -X GET http://localhost:8001/chain
$ curl -X GET http://localhost:8002/chain

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