Download Ruby: An introduction

Ruby: An introduction - Who am I?
Ruby: An introduction
Presented by:
Maciej Mensfeld
senior ruby [email protected]
lead ruby [email protected]
[email protected]
dev.mensfeld.pl
github.com/mensfeld
Maciej Mensfeld
1/23
Ruby: An introduction – please…
Ruby: An introduction
Please…
• …ask me to slow down, if I speak to quickly;
• …ask me again, if I forget;
• …ask questions, if anything i say is not clear;
• …feel free to share your own observations
Maciej Mensfeld
2/23
Ruby: An introduction – What is Ruby?
Ruby WT*?
Ruby pictures
Maciej Mensfeld
3/23
Ruby: An introduction – What is Ruby?
What is Ruby?
•
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•
•
•
•
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Pure object-oriented programming language (even the number 1 is
an instance of class);
Created by Yukihiro Matsumoto in 1993;
Freely available and open-source;
Syntax is readable and easy to learn;
Being used for text processing, web apps, general system
administration, and AI and math research.
Can be extended with Ruby or low-level C;
Really helpful community;
Maciej Mensfeld
4/23
Ruby: An introduction – What I love in Ruby?
Clarity not ceremony – Main program
Java:
public class HelloWorld{
public static void main(String args){
System.out.println(„Hello World”);
}
}
Ruby:
puts „Hello World”
Try it
out!
Maciej Mensfeld
5/23
Ruby: An introduction – What I love in Ruby?
Expressive syntax && objects, objects, objects…
3.times { puts „Ruby is cool”}
[„Maciek”, „John”, „Anna”].first #=> „Maciek”
[„Maciek”, „John”, „Anna”].last #=> „Anna”
attr_accessor :name
„Anna”.class #=> String
nil.class #=> NilClass
1.class #=> Integer
{}.class #=> Hash
[].class #=> Array
self.class #=> Object
(0..9).class #=> Range
Maciej Mensfeld
6/23
Ruby: An introduction – syntax
Ruby syntax – hello world as a function
Hello World!
puts „Hello World!”
Try it
out!
Hello
YourName!
puts „Hello #{name}”
def h
puts „Hello World!”
end
h => „Hello World!”
def h(name=„World”)
puts „Hello #{name}!”
end
h („Maciek”)=> „Hello Maciek!”
Maciej Mensfeld
7/23
Ruby: An introduction – syntax
Ruby syntax – classes, methods, objects
Try it
out!
Hello YourName!
as an object
# Comments starts with „#”
class Messenger
def initialize(name)
# instance variables starts with „@”
@name = name
end
public
def hello
puts „Hello #{@name }!”
end
end
msg = Message.new(„Maciek”)
msg.hello #=> „Hello Maciek!”
Maciej Mensfeld
8/23
Ruby: An introduction – syntax
Ruby syntax – arrays, hashes (dictionaries)
Arrays
names = [‘Maciek’, ‘John’, ‘Freddy’]
names.length #=> 3
debts.length #=> 2
Hashes
Maciej Mensfeld
debts={„Maciek”=>1, „John”=> 10}
9/23
Ruby: An introduction – syntax
Ruby syntax – loops
Ruby:
friends.each{|friend| puts friend }
C:
for(i=0; i<number_of_elements;i++)
{
print element[i]
}
Try it
out!
10.times {|i| puts i }
10.downto(1){|i| puts i }
There is no standard „for” loop in Ruby!
Maciej Mensfeld
10/23
Ruby: An introduction – syntax
Ruby craziness - symbols
When you ask someone : what are symbols in
Ruby? Most programmers will say: they simple are!
A symbol in Ruby is an instance of the class Symbol.
A symbol is defined by prefixing a colon with an
identifier. :name, :id, :user
Symbols are most commonly used in creating hashes:
h = {:name => "Jayson", :email => „[email protected]"}
OMG
symbols are
so weird…
The advantage in using symbols is the efficient use of memory.
Maximum space taken by a symbol is never more than the space taken
by an integer. This is because internally symbol is stored as an integer.
In case of strings the memory space depends on the size of the string.
Maciej Mensfeld
11/23
Ruby: An introduction – syntax
Ruby craziness - symbols
Also whenever a string is used in the program, a
new instance is created. But for symbols, same
identifier points to the same memory location!
puts "name".object_id
puts "name".object_id
puts :name.object_id
puts :name.object_id
Try it
out!
Compare:
puts "name".object_id == "name".object_id
puts :name.object_id == :name.object_id
Maciej Mensfeld
12/23
Ruby: writing some cool stuff
Web crawler!
Enough theory!
Let’s be pragmatic!
Fetch and store urls
Simple web crawler
requirements
Search 4 keywords
(support regexp)
Don’t revisit urls
Print results
Maciej Mensfeld
23
Ruby: writing some cool stuff
Web crawler – page content parser
What do we need?
Maciej Mensfeld
Parser
Crawler
Extracts data from page
content
Crawl all available pages
23
Ruby: writing some cool stuff
Simple parser – 13LOC
attr_reader – set instance variable as readonly from the outside
attr_accessor – make instanca variable R/W from the outside
Maciej Mensfeld
23
Ruby: writing some cool stuff
Simple parser – 13LOC
@keyword.is_a?(String) ? @keyword.downcase : @keyword
Just like in C and PHP:
condition_true ? if true do smthng : if false do smthng
Try it
out!
Maciej Mensfeld
true ? puts(„I’m true!”) : puts(„I’m false!”)
false ? puts(„I’m true!”) : puts(„I’m false!”)
16/23
Ruby: writing some cool stuff
Simple parser – 13LOC
Try it
out!
Maciej Mensfeld
17/23
Ruby: writing some cool stuff
Crawler – How should it work?
Try to download
page
Select another
page
No
Success?
Yes
Mark page as
visited
Maciej Mensfeld
Do something with result
(parse, send, etc)
18/23
Ruby: writing some cool stuff
Crawler – 37LOC
Try it
out!
We will check only pages with specified extensions
(html, asp, php, etc)
Add our start url to a @new_urls array (basicly create @new_urls array
with one address in it)
No pages where visited yet – so @visited_urls = [] (empty array)
Maciej Mensfeld
19/23
Ruby: writing some cool stuff
Crawler – read page in Ruby
Reading pages in Ruby is easy!
Try it
out!
Mark page as visited (add it to @visited_urls array)
Load current content page (parse URL and address)
Catch any type of exception (404, 500, etc) – mark page as visited so we
don’t go there again and return false
Maciej Mensfeld
20/23
Ruby: writing some cool stuff
Crawler – extract URLs
Reading pages in Ruby is easy!
Try it
out!
Use URI.extract method to extract all urls from @current_content
Check if URL is valid (try to parse it and check extension)
If anything failes – assume that this URL is incorrect
Maciej Mensfeld
21/23
Ruby: writing some cool stuff
Crawler – run crawler!
Try it
out!
Maciej Mensfeld
22/23
Ruby: writing some cool stuff
THX
Presented by:
Maciej Mensfeld
[email protected]
dev.mensfeld.pl
github.com/mensfeld
Maciej Mensfeld
22/30