Author Archives: Jack Schultz

How to Build Your Own Blockchain Part 4.2 — Ethereum Proof of Work Difficulty Explained

We’re back at it in the Proof of Work difficulty spectrum, this time going through how Ethereum’s difficulty changes over time. This is part 4.2 of the part 4 series, where part 4.1 was about Bitcoin’s PoW difficulty, and the following 4.3 will be about jbc’s PoW difficulty.

TL;DR

To calculate the difficulty for the next Ethereum block, you calculate the time it took to mine the previous block, and if that time difference was greater than the goal time, then the difficulty goes down to make mining the next block quicker. If it was less than the time goal, then difficulty goes up to attempt to mine the next block quicker.

There are three parts to determining the new difficulty: offset, which determines the standard amount of change from one difficulty to the next; sign, which determines if the difficulty should go up or down; and bomb, which adds on extra difficulty depending on the block’s number.

These numbers are calculated slightly differently for the different forks, Frontier, Homestead, and Metropolis, but the overall formula for calculating the next difficulty is

target = parent.difficulty + (offset * sign) + bomb

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Pre notes

For the following code examples, this will be the class of the block.

class Block():
  def __init__(self, number, timestamp, difficulty, uncles=None):
    self.number = number
    self.timestamp = timestamp
    self.difficulty = difficulty
    self.uncles = uncles

The data I use to show the code is correct was grabbed from Etherscan.

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How to Build Your Own Blockchain Part 4.1 — Bitcoin Proof of Work Difficulty Explained

If you’re wondering why this is part 4.1 instead of part 4, and why I’m not talking about continuing to build the local jbc, it’s because explaining Bitcoin’s Proof of Work difficulty at a somewhat lower level takes a lot of space. So unlike what this title says, this post in part 4 is not how to build a blockchain. It’s about how an existing blockchain is built.

My main goal of the part 4 post was to have one section on the Bitcoin PoW, the next on Ethereum’s PoW, and finally talk about how jbc is going to run and validate proof or work. After writing all of part 1 to explain how Bitcoin’s PoW difficulty, it wasn’t going to fit in a single section. People, me included, tend get bored in the middle reading a long post and don’t finish.

So part 4.1 will be going through Bitcoin’s PoW difficulty calculations. Part 4.2 will be going through Ethereum’s PoW calculations. And then part 4.3 will be me deciding how I want the jbc PoW to be as well as doing time calculations to see how long the mining will take.

The sections of this post are:

  1. Calculate Target from Bits
  2. Determining if a Hash is less than the Target
  3. Calculating Difficulty
  4. How and when block difficulty is updated
  5. Full code
  6. Final Questions

TL;DR

The overall term of difficulty refers to how much work has to be done for a node to find a hash that is smaller than the target. There is one value stored in a block that talks about difficulty — bits. In order to calculate the target value that the hash, when converted to a hex value has to be less than, we use the bits field and run it through an equation that returns the target. We then use the target to calculate difficulty, where difficulty is only a number for a human to understand how difficult the proof of work is for that block.

If you read on, I go through how the blockchain determines what target number the mined block’s hash needs to be less than to be valid, and how that target is calculated.

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Calculate Target from Bits

In order to go through Bitcoin’s PoW, I need to use the values on actual blocks and explain the calculations, so a reader can verify all this code themselves. To start, I’m going to grab a random block number to work with and go through the calculations using that.

>>>import random
>>> random.randint(0, 493928)
111388

Block number 11138 it is! Back in time to March of 2011 we go.

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How to Build Your Own Blockchain Part 3 — Writing Nodes that Mine and Talk

Hello all and welcome to Part 3 of building the JackBlockChain — JBC. Quick past intro, in Part 1 I coded and went over the top level math and requirements for a single node to mine its own blockchain; I create new blocks that have the valid information, save them to a folder, and then start mining a new block. Part 2 covered having multiple nodes and them having the ability to sync. If node 1 was doing the mining on its own and node 2 wanted to grab node 1’s blockchain, it can now do so.

For Part 3, read the TL;DR right below to see what we got going for us. And then read the rest of the post to get a (hopefully) great sense of how this happened.

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TL;DR

Nodes will compete to see who gets credit for mining a block. It’s a race! To do this, we’re adjusting mine.py to check if we have a valid block by only checking a section of nonce values rather than all the nonces until a match. Then APScheduler will handle running the mining jobs with the different nonce ranges. We shift the mining to the background if we want node.py to mine as well as being a Flask web service. By the end, we can have different nodes that are competing for first mining and broadcasting their mined blocks!

Before we start, here’s the code on Github if you want to checkout the whole thing. There are code segments on here to illustrate about what I did, but if you want to see the entire code, look there. The code works for me, but I’m also working on cleaning everything up, and writing a usable README so people can clone and run it themselves. Twitter, and contact if you want to get in contact.

Mining with APScheduler and Mining Again

The first step here is to adjust mining to have the ability to stop if a different node has found the block with the index that it’s working on. From Part 1, the mining is a while loop which will only break whenz it finds a valid nonce. We need the ability to stop the mining if we’re notified of a different node’s success.

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How to Build Your Own Blockchain Part 2 — Syncing Chains From Different Nodes

Welcome to part 2 of the JackBlockChain, where I write some code to introduce the ability for different nodes to communicate.

Initially my goal was to write about nodes syncing up and talking with each other, along with mining and broadcasting their winning blocks to other nodes.   In the end, I realized that the amount of code and explanation to accomplish all of that was way too big for one post. Because of this, I decided to make part 2 only about nodes beginning the process of talking for the future.

By reading this you’ll get a sense of what I did and how I did it. But you won’t be seeing all the code. There’s so much code involved that if you’re looking for my total implementation you should look at the entire code on the part-2 branch on Github.

Like all programming, I didn’t write the following code in order. I had different ideas, tried different tactics, deleted some code, wrote some more, deleted that code, and then ended up with the following.

This is totally fine! I wanted to mention my process so people reading this don’t always think that someone who writes about programming does it in the sequence they write about it. If it were easy to do, I’d really like to write about different things I tried, bugs I had that weren’t simple to fix, parts where I was stuck and didn’t easily know how to move forward.

It’s difficult to explain the full process and I assume most people reading this aren’t looking to know how people program, they want to see the code and implementation. Just keep in mind that programming is very rarely in a sequence.

Twitter, contact, and feel free to use comments below to yell at me, tell me what I did wrong, or tell me how helpful this was. Big fan of feedback.

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TL;DR

If you’re looking to learn about how blockchain mining works, you’re not going to learn it here. For now, read part 1 where I talk about it initially, and wait for more parts of this project where I go into more advanced mining.

At the end, I’ll show the way to create nodes which, when running, will ask other nodes what blockchain they’re using, and be able to store it locally to be used when they start mining. That’s it. Why is this post so long? Because there is so much involved in building up the code to make it easier to work with for this application and for the future.

That being said, the syncing here isn’t super advanced. I go over improving the classes involved in the chain, testing the new features, creating other nodes simply, and finally a way for nodes to sync when they start running.

For these sections, I talk about the code and then paste the code, so get ready.

Expanding Block and adding Chain class

This project is a great example of the benefits of Object Oriented Programming. In this section, I’m going to start talking about the changes to the Block class, and then go in to the creation of the Chain class.

The big keys for Blocks are:

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How to Build Your Own Blockchain Part 1 — Creating, Storing, Syncing, Displaying, Mining, and Proving Work

I can actually look up how long I have by logging into my Coinbase account, looking at the history of the Bitcoin wallet, and seeing this transaction I got back in 2012 after signing up for Coinbase. Bitcoin was trading at about $6.50 per. If I still had that 0.1 BTC, that’d be worth over $500 at the time of this writing. In case people are wondering, I ended up selling that when a Bitcoin was worth $2000. So I only made $200 out of it rather than the $550 now. Should have held on.

Thank you Brian.

Despite knowing about Bitcoin’s existence, I never got much involved. I saw the rises and falls of the $/BTC ratio. I’ve seen people talk about how much of the future it is, and seen a few articles about how pointless BTC is. I never had an opinion on that, only somewhat followed along.

Similarly, I have barely followed blockchains themselves. Recently, my dad has brought up multiple times how the CNBC and Bloomberg stations he watches in the mornings bring up blockchains often, and he doesn’t know what it means at all.

And then suddenly, I figured I should try to learn about the blockchain more than the top level information I had. I started by doing a lot of “research”, which means I would search all around the internet trying to find other articles explaining the blockchain. Some were good, some were bad, some were dense, some were super upper level.

Reading only goes so far, and if there’s one thing I know, it’s that reading to learn doesn’t get you even close to the knowledge you get from programming to learn. So I figured I should go through and try to write my own basic local blockchain.

A big thing to mention here is that there are differences in a basic blockchain like I’m describing here and a ‘professional’ blockchain. This chain will not create a crypto currency. Blockchains do not require producing coins that can be traded and exchanged for physical money. Blockchains are used to store and verify information. Coins help incentive nodes to participate in validation but don’t need to exist.

The reason I’m writing this post is 1) so people reading this can learn more about blockchains themselves, and 2) so I can try to learn more by explaining the code and not just writing it.

In this post, I’ll show the way I want to store the blockchain data and generate an initial block, how a node can sync up with the local blockchain data, how to display the blockchain (which will be used in the future to sync with other nodes), and then how to go through and mine and create valid new blocks. For this first post, there are no other nodes. There are no wallets, no peers, no important data. Information on those will come later.

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TL;DR

If you don’t want to get into specifics and read the code, or if you came across this post while searching for an article that describes blockchains understandably, I’ll attempt to write a summary about how a blockchains work.

At a super high level, a blockchain is a database where everyone participating in the blockchain is able to store, view, confirm, and never delete the data.

On a somewhat lower level, the data in these blocks can be anything as long as that specific blockchain allows it. For example, the data in the Bitcoin blockchain is only transactions of Bitcoins between accounts. The Ethereum blockchain allows similar transactions of Ether’s, but also transactions that are used to run code.

Slightly more downward, before a block is created and linked into the blockchain, it is validated by a majority of people working on the blockchain, referred to as nodes. The true blockchain is the chain containing the greatest number of blocks that is correctly verified by the majority of the nodes. That means if a node attempts to change the data in a previous block, the newer blocks will not be valid and nodes will not trust the data from the incorrect block.

Don’t worry if this is all confusing. It took me a while to figure that out myself and a much longer time to be able to write this in a way that my sister (who has no background in anything blockchain) understands.

If you want to look at the code, check out the part 1 branch on Github. Anyone with questions, comments, corrections, or praise (if you feel like being super nice!), get in contact, or let me know on twitter.

Step 1 — Classes and Files

Step 1 for me is to write a class that handles the blocks when a node is running. I’ll call this class Block. Frankly, there isn’t much to do with this class. In the __init__ function, we’re going to trust that all the required information is provided in a dictionary. If I were writing a production blockchain, this wouldn’t be smart, but it’s fine for the example where I’m the only one writing all the code. I also want to write a method that spits out the important block information into a dict, and then have a nicer way to show block information if I print a block to the terminal.

class Block(object):
  def __init__(self, dictionary):
  '''
    We're looking for index, timestamp, data, prev_hash, nonce
  '''
  for k, v in dictionary.items():
    setattr(self, k, v)
  if not hasattr(self, 'hash'): #in creating the first block, needs to be removed in future
    self.hash = self.create_self_hash()

  def __dict__(self):
    info = {}
    info['index'] = str(self.index)
    info['timestamp'] = str(self.timestamp)
    info['prev_hash'] = str(self.prev_hash)
    info['hash'] = str(self.hash)
    info['data'] = str(self.data)
    return info

  def __str__(self):
    return "Block<prev_hash: %s,hash: %s>" % (self.prev_hash, self.hash)

When we’re looking to create a first block, we can run the simple code.

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NPR Sunday Puzzle Solving, And Other Baby Name Questions

If you have a long drive and no bluetooth or aux cord to listen to podcasts, NPR is easily the best alternative. Truck drivers agree with this statement no matter their overall views. For me, this was the case when driving home to Milwaukee from Ann Arbor where I went to a college friend’s wedding.

While driving back I listened to NPR and heard Weekend Edition Sunday and their Sunday Puzzle pop up. If you haven’t heart of it before, at the end of every week’s episode they state a puzzle. Throughout the next week listeners can submit their answer and one random correct submitter is chosen to be recorded doing a mini puzzle on air.

The puzzle they stated for the week after the wedding was as follows:

Think of a familiar 6-letter boy’s name starting with a vowel. Change the first letter to a consonant to get another familiar boy’s name. Then change the first letter to another consonant to get another familiar boy’s name. What names are these?

They’ve already released the show for this question (I didn’t win of course) so I figure I can write about how I found out the answer!

Solving The Name Question

First step as always for these types of posts is gathering the required list of familiar boy’s names.  Searching on Google for lists will show that there are a ton of sites which exist try to SEO themselves for the money. When scraping, you should to poke around and make sure to choose the post that has the correct data as well as being the most simple to gather. I went with this one.

Since there’s only one page with the data, there’s no need to use the requests library to scrape the different pages. So clicking save html file to the folder you’re programming in is the best way to get the data.

The scraping code itself is pretty simple.

from bs4 import BeautifulSoup

filename = 'boy_names.html'
vowels = ('A', 'E', 'I', 'O', 'U')

vowel_starters = []
consonant_starters = []

with open(filename, 'r') as file:
  page = file.read()
  html = BeautifulSoup(page.replace('\n',''), 'html.parser')
  for name_link in html.find_all("li", class_="p1"):
    name = name_link.text
    first_letter = name[0]
    if len(name) == 6:
      if first_letter in vowels:
        vowel_starters.append(name)
      else:
        consonant_starters.append(name)

for vname in vowel_starters:
  cname_same = []
  for cname in consonant_starters:
    if vname[1:] == cname[1:]:
      cname_same.append(cname)
  if cname_same:
    print vname
    for match in cname_same:
      print match

And the results are…

Austin, Justin, Dustin

Justin and Dustin rhyme which makes it more simple to realize that they match, but Austin isn’t exactly on the same page. If I didn’t have the code, zero chance I’d have gotten this correct.

That’s it right? Nope, I have all the code, I figured I should check to see if there’s a match for girls names with that same rules. All there was to do is save the popular girl names to the same folder, change the filename to ‘girl_names.html’, run the code, and we’ll get Ariana and Briana. A and B are the starting letters, and if Criana was a popular name (at this moment), we’d be good to for the full 3 name answers.

By going through this part, I came up with some other fun questions that could be answered with this list of names, and the rest of the post is about those.

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Web Scraping with Python — Part Two — Library overview of requests, urllib2, BeautifulSoup, lxml, Scrapy, and more!

Welcome to part 2 of the Big-Ish Data general web scraping writeups! I wrote the first one a little bit ago, got some good feedback, and figured I should take some time to go through some of the many Python libraries that you can use for scraping, talk about them a little, and then give suggestions on how to use them.

If you want to check the code I used and not just copy and paste from the sections below, I pushed the code to github in my bigishdata repo. In that folder you’ll find a requirements.txt file with all the libraries you need to pip install, and I highly suggest using a virtualenv to install them. Gotta keep it all contained and easier to deploy if that’s the type of project you’re working on. On this front, also let me know if you’re running this and have any issues!

Overall, the goal of the scraping project in this post is to grab all the information – text, headings, code segments and image urls – from the first post on this subject. We want to get the headings (both h1 and h3), paragraphs, and code sections and print them into local files, one for each tag. This task is very simple overall which means it doesn’t require super advanced parts of the libraries. Some scraping tasks require authentication, remote JSON data loading, or scheduling the scraping tasks. I might write an article about other scraping projects that require this type of knowledge, but it does not apply here. The goal here is to show basics of all the libraries as an introduction.

In this article, there’ll be three sections. First, I’ll talk about libraries that execute http requests to obtain HTML. Second, I’ll talk about libraries that are great for parsing HTML to allow you to scrape the data. Third, I’ll write about libraries that perform both actions at once. And if you have more suggestions of libraries to show, let me know on twitter and I’ll throw them in here.

Finally, a couple notes:

Note 1: There are many different ways of web scraping. People like using different methods, different libraries, different code structures, etc. I understand that.  I recognize that there are other useful methods out there – this is what I’ve found to be successful over time.

Note 2: I’m not here to tell you that it’s legal to scrape every website. There are laws about what data is copyrighted, what data that is owned by the company, and whether or not public data is actually legal to scrape. You might have to check things like robots.txt, their Terms of Service, maybe a frequently asked questions page.

Note 3: If you’re looking for data, or any other data engineering task, get in contact and we’ll see what I can do!

Ok! That all being said, it’s time to get going!

Requesting the Page

The first section here is showing a few libraries that can hit web servers and ask nicely for the HTML.

For all the examples here, I request the page, and then save the HTML in a local file. The other note on this section is that if you’re going to use one of these libraries, this is part one of the scraping! I talked about that a lot in the first post of this series, how you need to make sure you split up getting the HTML, and then work on scraping the data from the HTML.

First library on the first section is the famous, popular, and very simple to use library, requests.

requests

Let’s see it in action.

import requests
url = "https://bigishdata.com/2017/05/11/general-tips-for-web-scraping-with-python/" 
params = {"limit": 48, 'p': 2} #used for query string (?) values
headers = {'user-agent' : 'Jack Schultz, bigishdata.com, contact@bigishdata.com'}
page = requests.get(url, headers=headers)
helpers.write_html('requests', page.text.encode('UTF-8'))

Like I said, incredibly simple.

Requests also has the ability to use the more advanced features like SSL, credentials, https, cookies, and more. Like I said, I’m not going to go into those features (but maybe later). Time for simple examples for an actual project.

Overall, even before talking about the other libraries below, requests is the way to go.

urllib / urllib2

Ok, time to ignore that last sentence in the requests section, and move on to another simple library, urllib2. If you’re using Python 2.X, then it’s very simple to request a single page. And by simple, I mean couple lines.

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