Learning Blockchain with Python

Personal learning project I built to understand how blockchains work under the hood.
It's written in Python using Flask and simulates core concepts like Proof of Work mining, transactions, basic consensus, and multi-node synchronization — all in a simple, readable structure.

This isn't production-ready — it's just me exploring how to actually build a blockchain from scratch, step by step.

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Project Structure

python-blockchain/
├── core/                  # Blockchain logic
│   └── blockchain.py
├── api/                   # REST API with Flask
│   └── routes.py
├── run.py                 # Main entrypoint
├── requirements.txt
└── README.md

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🚀 How to Run

1. Install dependencies:

pip install -r requirements.txt

2. Launch multiple nodes:

python run.py 5001
python run.py 5002
python run.py 5003

3. Use /connect_node and /replace_chain to sync them.

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📡 Endpoints Overview

Method	Endpoint	What it does
GET	/mine_block	Mines a block with PoW
GET	/get_chain	Returns the full chain
GET	/is_valid	Validates the chain
POST	/add_transaction	Adds a new transaction (JSON: sender, receiver, amount)
POST	/connect_node	Connects other nodes (JSON: list of node URLs)
GET	/replace_chain	Syncs with the longest valid chain among connected nodes

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📦 Sample Payloads

POST /add_transaction

{
  "sender": "Alice",
  "receiver": "Bob",
  "amount": 50
}

POST /connect_node

{
  "nodes": [
    "http://127.0.0.1:5002",
    "http://127.0.0.1:5003"
  ]
}

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🔁 Node Sync Tip

To sync multiple nodes:

1. Run /connect_node from one of them
2. Call /replace_chain on the others to update to the longest valid chain