Category:I704 Ruby

From EIK wiki

About this course

This course teaches the Ruby programming language. By the end of the course you'll hopefully have a good understanding of:

  • the basics of Ruby,
  • tools commonly used in the Ruby ecosystem,
  • written a few small Ruby applications,
  • know about unit testing,
  • know how to use third-party code (Ruby gems),
  • know how to write web applications using Ruby.

Lecture Recordings

You can find recordings of the lectures here:

https://echo360.e-ope.ee/ess/portal/section/b02ab032-010b-4111-a53d-2f5a47db1fdd

About yourself

To help me make this course interesting for you and meet your expectations, please fill out this survey if you haven't done so already:

http://bit.ly/2jxwrs8

Reference material

Here you find a list of useful links to things that have been mentioned or discussed during the lectures:

Editors/IDEs

Grading

Students develop several small projects during the lectures and independent study. At the end of the course students pick one of their projects and are assigned a feature request to implement in their project and a set of questions about the code in their project.

Points are awarded for the following:

  • 50 points for a working implementation of the feature request
  • 40 points for an implementation of the feature request that works only for expected inputs
  • 20 points for a running unfinished implementation (i.e. feature not fully implemented, but the program still runs)
  • 10 points for an unfinished implementation (i.e. feature not fully implement and the program does not run).
  • 20 points for providing automated tests for their implementation
  • 10 points for proper use of version control
  • 10 points for a having a README describing your project
  • 10 points for adhering to common Ruby coding standards
  • 10 points for structuring your project as a Rubygem
  • 20 points for answering 80% of the questions correctly

The student needs at least 60 points in order to pass the course.

Proper use of version control

Point value: 10

These points are awarded if:

  1. you keep your code in a git repository
  2. a single commit represents a single logical step in the development process (e.g. adding a test and the code to make it pass, fixing a single bug, refactoring one area of the code, etc)
  3. most commit messages follow the guidelines for good commit messages (see reference material below)

Reference material

Having a README

Point value: 10

These points are awarded if:

  1. your project has a file called README.md in your project's root directory
  2. the README.md file contains a description of: what your program does, how to install it and how to run it

Adhering to common Ruby coding standards

Point value: 10

These points are awarded if:

  1. running rubocop with the default configuration in your project produces no errors

Reference material

  • Rubocop Basic Usage. Hint: You can run Rubocop with the --auto-correct option to automatically fix some of the problems Rubocop discovered.

Providing automated tests

Point value: 20

These points are awarded if:

  1. running bundle exec rake test runs your test suite
  2. your test suite has no failing tests
  3. your test suite contains at least one meaningful test, testing your program's logic

Reference material

Structuring your project as a Rubygem

Point value: 10

These points are awarded if:

  1. your project directory structure matches the structure created by bundle gem NAME_OF_YOUR_PROJECT
  2. additional dependencies are specified in the .gemspec file of your project

If your project is using a framework with strong conventions, such as Ruby on Rails, these points are awarded if you place your code according to the conventions of the framework.

Reference material


Answering 80% of the questions correctly

Point value: 20

You will be asked 3 to 5 questions about your project, testing your understanding of what is happening in the code.

These points are awarded if:

  1. you answer 80% or more of the questions correctly

2017-02-02: Lecture and Lab

Analyzing bank statements

Given the following contents of a file called input.csv

   transaction_id,date,amount,credit
   1,2017-02-02 12:40,1.30,debit
   2,2017-02-02 12:55,2.50,debit
   3,2017-02-02 13:00,1.00,credit

Goal: find the amount of money left on your bank account.

Steps:

  1. read the data line by line
  2. analyze each line to find out whether it's credit or debit and the amount of money
  3. add all the debit transaction amounts (money lost)
  4. add all the credit transaction amounts (money gained)
  5. Output money gained - money lost

Our code so far:

 1 File.open('input.csv', 'r') do |the_file|
 2   lines = the_file.readlines.map do |line|
 3     line.chomp.split(',')
 4   end
 5   lines = lines[1..-1]
 6   debit_total = ''
 7   lines.each do |line|
 8     debit_total = debit_total + line[2]
 9   end
10   puts debit_total
11 end

2017-02-09 Lecture

 1 require 'minitest'
 2 require 'minitest/autorun'
 3 
 4 class BankAccount
 5   class Error < StandardError; end
 6   class BalanceNegative < Error; end
 7 
 8   def initialize
 9     @balance = 0
10   end
11 
12   def deposit!(amount)
13     increse_balance!(amount)
14 
15     self
16   end
17 
18   def withdraw!(amount)
19     if enough_money?(amount)
20       reduce_balance!(amount)
21     else
22       raise StandardError, 'Not enough money!'
23     end
24 
25     self
26   end
27 
28   def balance
29     @balance
30   end
31 
32   private
33 
34   def enough_money?(amount)
35     balance >= amount
36   end
37 
38   def reduce_balance!(amount)
39     @balance = @balance - amount
40   end
41 
42   def increse_balance!(amount)
43     @balance = @balance + amount
44   end
45 
46 end
47 
48 class BankAccountTest < Minitest::Test
49   def setup
50     @account = BankAccount.new
51   end
52 
53   def test_if_decreses_the_balance_when_withdrawing_money
54     @account.deposit!(101).withdraw!(50)
55     assert_equal 51, @account.balance
56   end
57 
58   def test_if_increses_the_balance_when_depositing_money
59     @account.deposit!(196583)
60     assert_equal 196583, @account.balance
61   end
62 
63   def test_if_account_does_not_go_in_to_negative
64     assert_raises BankAccount::BalanceNegative do
65       @account.deposit!(1).withdraw!(20)
66     end
67   end
68 
69   def test_it_raises_bank_account_error_when_withdrawing_too_much_money
70     @account.deposit!(1).withdraw!(20)
71   rescue BankAccount::Error => err
72     assert true, 'everything is ok'
73   end
74 end

2017-02-16 Lecture and Lab: using modules and bundler

Modules in Ruby

  • Modules are a collection of methods that can be included in another class
  • By including the module in a class, objects belonging to that class get access to the methods defined in the module
  • If multiple included modules define the same method, the method from the module that was included last counts

Example

module ModuleExample
  def foo
    'foo'
  end
end

# Including modules binds their methods to the class instances
# Extending modules binds their methods to the class itself

class Person
  include ModuleExample
end

class Book
  extend ModuleExample
end

Person.foo     # => NoMethodError: undefined method `foo' for Person:Class
Person.new.foo # => 'foo'
Book.foo       # => 'foo'
Book.new.foo   # => NoMethodError: undefined method `foo'

Structuring a project with bundler

  • bundler is a Ruby program for managing dependencies in your ruby project
  • bundler also helps you with creating a template for a project
  • redistributable projects/libraries are called "gems" in ruby
  • You can start your own project by running bundle gem YOUR_PROJECT_NAME_HERE. Replace YOUR_PROJECT_NAME_HERE with the lower-cased name of your project.

Example structure of a project, as generated by bundler

$ tree
.
├── bin
│   ├── console
│   └── setup
├── exe
│   └── hello-world
├── Gemfile
├── Gemfile.lock
├── I704.gemspec
├── lib
│   ├── I704
│   │   ├── bank_account.rb
│   │   └── version.rb
│   └── I704.rb
├── LICENSE.txt
├── Rakefile
├── README.md
└── test
    ├── I704
    │   └── bank_account_test.rb
    ├── I704_test.rb
    └── test_helper.rb

6 directories, 15 files


  • exectuables that users of your gem should be able to run go into the exe directory
  • add dependencies in your .gemspec file. After adding a dependency, run bundle install to install the dependency on your computer.


Rule of thumb: put your code into the lib/YOUR_PROJECT_NAME directory, one file per class (like bank_account.rb in the example above)

2017-03-02 Lecture & Lab

Word count example

text = "Burning Rangers is a 1998 3D action video game developed by Sonic Team and published by Sega for the Sega Saturn. The game is set in a futuristic society threatened by frequent fires. Players control one of an elite group of firefighters, the Burning Rangers, who extinguish the fires and rescue civilians from burning buildings. Most of the tasks the players complete are centred around collecting energy crystals used to transport civilians to safety. Development began shortly after the release of Christmas Nights in November 1996, when Yuji Naka started working on a game focused on saving people rather than killing them. Sonic Team chose the themes of firefighting and heroism. Burning Rangers received mostly positive reviews, especially for the game's soundtrack and audio. Responses to the graphics were mixed; while some critics asserted that the game had the best visuals on the Saturn, others faulted its poor collision detection and occasional glitching. The game was among the final five Saturn titles released in America."

words = text.split(' ')

words_without_punctuation = words.map do |word|
  word.sub(/[.,;?!:]/, '').downcase
end

word_count = words_without_punctuation.reduce({}) do |result, word|
  if result.key?(word)
    result[word] = result[word] + 1
    # also possible: result[word] += 1
  else
    result[word] = 1
  end

  result
end

puts word_count

2017-03-09 lecture

Using locks

require 'thread'

# [1, 2, ..., 100]
# [t1, t2, ..., t100]

# Lock / Mutex (mutual exclusion)
# Queue

lock = Mutex.new
threads = (1..100).map do |number|
  Thread.new do
    sleep 0.5

    lock.lock
    puts number
    lock.unlock

    lock.synchronize do
      if number == 1
        sleep 5
      end
      puts number
    end
  end
end

threads.each do |thread|
  thread.join
end

Using a queue

require 'thread'

# Queue

queue = Queue.new

printer = Thread.new do
  loop do
    number = queue.pop
    puts number
  end
end

threads = (1..100).map do |number|
  Thread.new do
    sleep 0.5
    queue.push number
  end
end

threads.each do |thread|
  thread.join
end

Using fork

shared_variable = 'untouched'
child_process_id = fork do
  puts "Running inside fork"
  puts "My process ID is #{$$}"
  shared_variable = 'touched'
end
Process.wait(child_process_id)
puts "In the parent #{$$}: shared_variable is #{shared_variable}"

Reference material: making HTTP requests in Ruby

  1. Require the "net/http" library in your program
  2. Use that library to make HTTP requests for fetching the HTML code behind a website
  3. See https://ruby-doc.org/stdlib-2.3.0/libdoc/net/http/rdoc/Net/HTTP.html for more examples of how to use this library
require 'net/http'
google_html = Net::HTTP.get(URI('http://google.com'))
# "<HTML><HEAD><meta http-equiv=\"content-type\" content=\"text/html;charset=utf-8\">\n<TITLE>302 Moved</TITLE></HEAD><BODY>\n<H1>302 Moved</H1>\nThe document has moved\n<A HREF=\"http://www.google.ee/?gfe_rd=cr&amp;ei=o6KlWKCGA9Oq8wfoq5OQAg\">here</A>.\r\n</BODY></HTML>\r\n"

# Now you can work with the HTML returned by the server

2017-03-16 Lecture

require 'pry'

##
#
#  NEVER RESCUE FROM Exception
#
#  HAVE AN ERROR CLASS FOR APPLICATION AND HAVE ALL APPLICATION ERRORS
#  INHERIT FROM IT.
##

# Options for error handling:
#
# 1. raise an exception
# 2. return a value describing the error
module ErrorHandling
  class Error < StandardError
  end

  class InvalidNumberError < Error
    def initialize(input)
      @input = input
    end

    attr_reader :input
  end

  class DivisionByZeroAttempted < Error
  end

  class WrongDayOfTheWeek < Error
  end

  class Application
    def run
      raise WrongDayOfTheWeek unless Date.today.monday?

      print("Enter a number: ")
      a = read_number
      print("Enter another number: ")
      b = read_number
      if b.zero?
        raise DivisionByZeroAttempted
      else
        puts "a / b = #{a / b}"
      end
    end

    def read_number
      input = $stdin.gets.chomp
      begin
        Float(input)
      rescue ArgumentError
        raise InvalidNumberError.new(input)
      end
    end
  end
end

Using return values for indicating errors

require 'pry'
module ErrorHandling
  class Application
    def run
      print("Enter a number: ")
      a = read_number
      until a != :invalid_input
        if a == :invalid_input
          puts "Not a number!"
        end
        a = read_number
      end

      print("Enter another number: ")
      b = read_number
      if b == :invalid_input
        puts "Not a number!"
        return
      end

      if b.zero?
        puts "You cannot divide by zero!"
        return
      end

      puts "a / b = #{a/b}"
    end

    def read_number
      input = $stdin.gets.chomp
      begin
        Float(input)
      rescue ArgumentError
        :invalid_input
      end
    end
  end
end

2017-03-23 Lecture

Using Struct

module Blog
  Post = Struct.new(:id, :title, :body_text) do
    def initialize(id:, title: 'no title', body_text: 'no body')
      super(id, title, body_text)
    end

    def validate
      errors = {}
      errors[:title] = :empty if title.empty?
      errors[:id] = :empty if id.empty?
      errors
    end
  end
end

first_article = Blog::Post.new(
  id: 'another-post'
)
puts first_article
puts first_article.validate

Reference material: parsing HTML using Nokogiri

Once you have received some HTML from a web server, you most likely want to analyze it. Use the library nokogiri for this. You can find installation instructions and tutorials here: http://www.nokogiri.org/tutorials/

Reference material: map and reduce

# map: takes a list and a block
#    returns: a list, where each element of the original list has been
#    passed to block
#
# reduce: takes list, an initial value and a block
#    returns: block applied to initial value and each element of the list

numbers = [1, 2, 3]
sum = numbers.reduce(0) do |current_sum, number|
  current_sum + number
end

puts "Sum: #{sum}"

####

numbers = [1, 2, 3]
sum = 0
numbers.each do |number|
  sum = sum + number
end

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