Free vs Paid Blockchain Courses What Should You Pick?

import hashlib
import json
import time

def make_block(data, prev_hash):
    block = {"time": time.time(), "data": data, "prev": prev_hash}
    text = json.dumps(block, sort_keys=True).encode()
    block["hash"] = hashlib.sha256(text).hexdigest()
    return block

chain = [make_block("genesis", "0" * 64)]
for item in ["Asha pays Ravi 10", "Ravi pays Meena 4"]:
    chain.append(make_block(item, chain[-1]["hash"]))

for b in chain:
    print(b["hash"][:16], "<-", b["prev"][:16], b["data"])

# Continuing from the hash chain tab
import hashlib, json

def valid(chain):
    for i in range(1, len(chain)):
        b = dict(chain[i])
        stored = b.pop("hash")
        recomputed = hashlib.sha256(json.dumps(b, sort_keys=True).encode()).hexdigest()
        if stored != recomputed or b["prev"] != chain[i - 1]["hash"]:
            return False
    return True

print(valid(chain))            # True
chain[1]["data"] = "Asha pays Ravi 1000"
print(valid(chain))            # False - tampering is detected

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Counter {
    uint256 public count;
    address public owner;

    event Incremented(address indexed by, uint256 newCount);

    constructor() {
        owner = msg.sender;
    }

    function increment() external {
        count += 1;                      // overflow checked since 0.8
        emit Incremented(msg.sender, count);
    }

    function reset() external {
        require(msg.sender == owner, "Only owner can reset");
        count = 0;
    }
}

What a good mentor checks in a smart contract:

[ ] Access control on sensitive functions (onlyOwner / require)
[ ] Input validation with require()
[ ] Events emitted for important state changes
[ ] No unbounded loops over user-controlled arrays
[ ] External calls made after state updates
[ ] Tests for normal and failure cases
[ ] Deployed and tested on a test network first

If a paid course does not teach this, free docs may be better.

# pip install cryptography
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives import hashes
from cryptography.exceptions import InvalidSignature

private_key = ec.generate_private_key(ec.SECP256K1())
public_key = private_key.public_key()

message = b"Transfer 5 tokens to Ravi"
signature = private_key.sign(message, ec.ECDSA(hashes.SHA256()))

try:
    public_key.verify(signature, message, ec.ECDSA(hashes.SHA256()))
    print("Signature valid")
except InvalidSignature:
    print("Signature invalid")

Suggested learning order for blockchain development

1. Programming fundamentals (JavaScript or Python)
2. Cryptography basics: hashing, keys, signatures
3. How a blockchain works: blocks, consensus, nodes
4. Smart contract language basics
5. Testing contracts with a development framework
6. Security patterns and common vulnerabilities
7. A small dApp on a test network
8. Code review and documentation

Does the course...                             Yes / No
Teach programming fundamentals first?           ___
Explain cryptography basics clearly?            ___
Include hands-on smart contract coding?         ___
Teach testing and security practices?           ___
Use test networks (no real money needed)?       ___
Offer mentor code reviews?                      ___
Show sample student projects?                   ___
Give a written fee and refund policy?           ___

Walk away if a blockchain course:

- Promises you will 'get rich' or earn fixed returns
- Focuses on trading tips rather than engineering
- Asks you to buy specific tokens or coins
- Uses pressure tactics or countdown timers
- Cannot name instructors or show their work
- Has no hands-on coding
- Guarantees a job

A course should teach skills, not sell investments.

My decision

Free resources I will use first:
1.
2.

Gaps after 4 weeks of free study:
-

Paid course considered: ______________
Does it fill my gaps?  Yes / No
Checklist score: ___ / 8
Final choice: ______________