How full-stack developers can make blockchain applications using Ethereum, Python, and JavaScript

1. Python,
Blockchain, and
Byte-Size Change
Portia Burton
@pkafei
PyDX 2016

2. Who am I?
My name is Portia Burton
I am a full-stack developer at the
Atlantic magazine
Became interested in blockchains
earlier this year
Not a cryptographic expert

3. What is a Blockchain?
A blockchain is a cross between a decentralized data store and bittorrent.

4. What is Bitcoin?
Type of Cryptocurrency
Creation based on paper by Satoshi Nakamoto titled
“Bitcoin: Peer-to-Peer Electronic Cash System”
Peer-to-peer which means transactions happen without
a third party. Alice can send money directly to Bob

5. Many Different Types of Cryptocurrencies

7. Bitcoin vs. Blockchain
Bitcoin is part of a blockchain
Blockchain is a digital ledger of transactions
Each transaction is cryptographically signed
Blockchains are trustless

8. Ethereum

10. Introduction to Ethereum
Ethereum is a programmable blockchain, every new blockchain spawned from
Ethereum has the same properties as Ethereum
Ethereum Virtual Machine is the low level machine language
Is Turing complete, unlike bitcoin which does not have looping capabilities
It also is aware of multiple states, unlike bitcoin which is only aware of two states
(spent and unspent)

11. Different Consensus Mechanisms
Proof of Work: Uses the Etash DAG algorithm. The Etash
DAG algorithm is based on Bitcoin’s the Dagger-Hashimoto
algorithm.
Proof of Stake: Proof of Stake is another way of validating. It
calculates the weight of the node, being proportional to its
computational resources. It’s less resource intensive than
Proof of Work.

12. Ethereum Chains (not all blockchains are the same)

14. Different Blockchains
Public blockchain: It is the official Ethereum chain that everyone can read and interact
with
Testnet blockchain: The official test chain of Ethereum. Good way to test contracts
without wasting real ether
Private blockchain: This is a blockchain that you can create yourself. This blockchain
can be freely accessed by others, or you can add addresses by invite only

15. Can an average developer build blockchain
applications?

16. Indeed, We Can!

17. But first, some more background

18. Smart Contracts (also known as DApps)

19. What is a Smart Contract?
Stored on the blockchain and executed
by code
Many smart contracts are written in
Solidity
Powered by gas which can be
computationally mined or purchased in
an exchange

20. Transaction: Signed data package that stores a message to be sent
GAS: the name for the execution fee that senders
of transactions need to pay for operations on
Ethereum blockchain
VALUE (field): The amount of wei to transfer
from sender to the recipient
STARTGAS (value): Representing the maximum
number of computational steps the transaction
execution is allowed to take
GASPRICE (value): Representing the fee the
sender is willing to pay for gas

21. Applications of Ethereum Blockchain of Smart Contracts
Self-executing legal contracts
Create “American Idol” where people can vote using generated tokens
Company boards can be ran virtually
Dropbox business model create and sell encrypted storage space
Predicting financial futures based on an oracle

22. Demo Time!

23. But what about Python?

24. Python Ethereum Client
● Regular commits
● Interacts with private blockchains AND the
official Ethereum blockchain
● Doesn’t download blocks as fast as Go or
Rust’s Ethereum client Parity

25. Actionable Ways Python Developers Can Interact
with Blockchain
1. Checkout BigchainDB
2. Contribute to Open Bazaar
3. Get web3 to interact with
Django or Flask

26. Bigchain DB
● This DB is actually in production (used
by ascribe.io)
● Hybrid of a database and blockchain
● NoSql datastore

27. BigchainDB compared to other data stores

28. Web3.js
JavaScript library that connects applications to a blockchain
The blockchain act as an alternative or complements the database
Currently web3 is used in the Javascript framework meteor but could be used in Flask
or Django

29. Why Should We Care?

30. Democracy and Governance

31. Democracy as We Know It Can Change
Voting can occur on the blockchain
Agreements will be controlled by code as opposed to legal contracts
Alternative way to keep track of identity
Laws and bill can be kept on the blockchain which will create a
permanent immutable record

32. Financial Industry

33. More Transparency, More Control
Money transfers can happen more seamlessly (less reliance on Western Union)
Transparent immutable ledger (do not have to trust banks with personal funds)
Access to capital for nations that lack a dependable banking system

34. Less Sharing in the Sharing Economy

35. Peer-to-Peer Profits
Ability to rent out rooms and rides without giving a portion of the profits to a
third-party company
Musicians earn more money when listeners stream their music
Alternative marketplace for creators (such as ascribe.io and OpenBazaar)

36. Solidity Contract Bugs
Transaction-Ordering Bug (TOD): Smart contract assumes a particular state of a
contract that doesn’t exist
Timestamp Dependence Bug: Asynchronous network is disconnected from a
synchronized global clock. Some contracts assume that network is on global contract
Unchecked Send: Most common exploit. Attacker elicits unexpected behavior from the
contract by calling if from a carefully constructed call-stack

37. https://ethereum.karalabe.com/talks/2016-hackethon.html#1
Smart Contract Bloopers

38. How to Get Started Today
Solidity Tutorial: https://solidity.readthedocs.io/en/develop/
Bootstrap Meteor App: https://github.com/SilentCicero/meteor-dapp-boilerplate
Example Dapps:
http://ethereum.stackexchange.com/questions/2940/where-can-i-find-some-solidity-smart-contract-source-code-examples
Command Line Interface of Interacting with the Ethereum Network: https://www.ethereum.org/cli
Meteor: https://www.meteor.com/

39. Contribute to Existing Blockchain Projects
OpenBazaar: https://github.com/OpenBazaar/OpenBazaar-Server/issues
BigChainDB: https://github.com/bigchaindb/bigchaindb/issues

40. Portia Burton
@pkafei
http://bit.ly/2dyGohH

41. Thank You!

42. References
1. http://ethdocs.org/en/latest/mining.html#what-is-mining
2. http://ethdocs.org/en/latest/frequently-asked-questions/frequently-asked-questions
.html#what-s-the-difference-between-account-and-wallet-contract
3. http://www.coindesk.com/making-sense-smart-contracts/
4. https://github.com/ethereum/go-ethereum/wiki/Command-Line-Options
5. http://www.ethdocs.org/en/latest/contracts-and-transactions/account-types-gas-an
d-transactions.html
6. https://blog.ethereum.org/2016/07/12/build-server-less-applications-mist/

43. 7.http://www.techrepublic.com/article/uk-government-using-blockchain-to-trac
k-welfare-spending/
8. https://github.com/ethereum/pyethapp
9. https://www.bigchaindb.com/whitepaper/bigchaindb-whitepaper.pdf