Friday, December 14, 2007

Learning Ruby from Python

I just started to pick up Ruby today (to install: sudo apt-get install ruby irb ri rubygems). Here are some things I learned along the way, coming from a Python mindset. The (very good and highly recommendable) references I looked at were (in order):
  1. Ruby in Twenty Minutes
  2. To Ruby From Python
  3. Ruby Essentials (free, on-line book)
  4. Important Language Features and Some Gotchas
Similarities
  • Brackets for arrays, braces for dictionaries (called hashes in Ruby)
  • Strong dynamic typing
  • Everything is an object, variables are just references
  • Exceptions are similar
  • No special line termination characters
  • # for single line comments
  • def to define a method, class to define a class
Differences
  • Interactive prompt: python => irb
  • Interactive prompt help: help(str.count) => help "String#count"
  • Interactive prompt reload: reload(foo) => load "foo.rb"
  • Command line docs: pydoc => ri
  • File extension: .py => .rb
  • Shebang line: #!/usr/bin/python => #!/usr/bin/env ruby
  • Indentation and blocks: : and tabs => either { } or end
  • Strings: immutable => mutable (can use freeze method for immutability)
  • Naming conventions: unenforced => enforced (ex. class names start with a capital letter, variables start with a lowercase letter)
  • Raw strings: r"blah" => 'blah'
  • Parantheses: mandatory => sometimes optional
  • Booleans: True, False => true, false
  • Null value: None => nil
  • Else-if statement: elif => elsif
  • Module import: import foo => require "foo"
  • Boolean conversion: 0, False, None and anything empty => Only nil and false
  • Doc generation: docstrings below things => regular comments above things
  • Output: print => puts (or print if you don't want a trailing newline)
  • Command line execution: python -c => ruby -e
  • Global Variables
  • Ranges: range(x,y) => x...y exclusive, x..y inclusive (.to_a to return array)
  • Slicing: arr[1:3] => arr[1...3] or arr[1..2] (inclusive)
  • Object initialization: __init__ => initialize
  • Object creation: a() => a.new
  • Ternary operator: if_true if statement else if_false => statement ? if_true : if_false
  • Substring matching: 'foo' in str => str['foo']
  • "Main": if __name__ == '__main__' => if __FILE__ == $0 ... end
Philosophical differences
  • Attribute access: direct access => method calls
    • Need getter and setter methods to access attribute outside class
  • Access permissions: convention by underscore => public, protected, private
  • Multiple inheritance: allowed => mixins
Stuff Ruby has that Python doesn't
  • Double quoted strings allow expression substitution #{} and escape sequences \t\n
  • You can re-open a class at any time and add more methods
  • Block comments: ==begin and ==end
  • Special variable characters (begins with...):
    • $ global
    • @ instance
    • [a-z_] local
    • [A-Z] constant (triggers warnings when reassigned)
    • @@ class
  • Arrays support some set operations
    • difference -
    • intersection &
    • union |
  • Method conventions (ends with...)
    • ! changes internal state of object
    • ? returns boolean
  • do keyword -- optional loop keyword (unless on single line)
  • Crazy for loop alternatives
  • General delimited strings
  • Case statement
  • Lots of options for string element access and string substitution and insertion
  • Regular expressions as first-order objects
  • Perl-like control flow constructs that can be tacked onto the end of an expression

No comments: