Young

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Young InterpretedPython, Ruby, JavaScript

• Susan Haynes
• 18 February 2008

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These three languages have a lot in common

• Dynamic typing -- variables have type, but the
  type can change during the course of execution
• Implicit typing -- if it walks like a duck,
  quacks like a duck, and swims like a duck ---
  its a duck.
• Interpreted -- Source code is not compiled then
  executed. Instead, the source is executed by the
  interpreter
• Released 92 - 95

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Theyre Really Different

• Extent of Object Orientation
• JavaScript is just barely OO
• Ruby is practically pure OO
• Python has extensive set of primitive sequential
  structures. JavaScript has String and Array
• JavaScript is intended to run in web pages and is
  integrated with the DOM
• Python and Ruby have lots of support for Web apps
  beyond displaying pages.

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Origins

• ruby released '95, author Yukihiro Matsumoto,
  open source
• python released '91, author Guido van Rossum,
  open source
• javascript released with Netscape 95. Originally
  developed by Brendan Eich (netscape) under the
  name mocha

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Questions

• Suitable for CS education?
• What are they good for?
• Coolness factor?

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What do I know?

• Not much. I havent done serious development in
  any of these languages -- only toy stuff.
• Plenty of experience learning a little bit about
  a lot of languages PL/1, Algol, Pascal, Fortran,
  basic, Lisp, C, C, Java, Ada, Prolog, APL,
  Javascript, various assemblers, scheme (squeak).

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Demos

• JavaScript using browser -(
• Python using IDLE or shell (python file)
• Ruby using irb or shell
• (ruby file.rb)

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White Space

• Javascript does not care about whitespace.
  EXCEPT! Multiple statements on a single line must
  be separated by
• Python uses white space to indicate nesting
  level.
• Ruby allows you to delete certain keywords
  depending on whitespace.

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Line termination

• Javascript is optional except when multiple
  statement per line (but everyone uses it)
• Python is optional. No one uses it
• Ruby is optional. No one uses it.

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Numbers

• Javascript number is a fundamental type (along
  with String, boolean and Object)
• Python number is a fundamental type, along with
  boolean, and various list types
• Ruby number is an object
• 3.zero? returns false
• 3.kind_of? Integer returns true
• 3.class return Fixnum
• 3.to_f returns 3.0

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Variable Names

• JavaScript -- the usual
• Python -- the usual
• Ruby --
• Local variables start with lower case or _
• Instance variables start with _at_
• Class variables start with _at__at_
• Globals start with

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Simple Python Program
Output enter integer 3 enter float -14.34 s1s2
3-14.34 n1n2 -11.34
First program first.py s1 raw_input(enter
integer ) s2 raw_input(enter float ) s3
s1 s2 print s1s2 s3 \n n1
int(s1) n2 float(s2) n3 n1n2 print n1n2
n3
Run this with Python and Idle import first then
reload(first) on subsequent changes
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Another simple Python program
Second program second.py x 10 y 3 print
type(x) , type(x) print type(y) ,
type(y) y int(y) print type(y) ,
type(y) dir()
Output import second type(x) int type(y) type(y) int __builtins__, __doc__,
__name__ first, n1, n2, sys, x, y
Notice use of type(), str() and dir() type(varX)
returns type of varX str(varY) any varY has a
nice string representation dir() lists all
known names
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Parallel Assignment

• Python, Ruby and JavaScript 1.7 have parallel
  assignments.
• Here is a python example (idle)

t (a, b, c) type(t) tuple t0 a t1 b type ( (x,
y, z) ) (x, y, z) t
x a y b
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Method Names

• JavaScript -- the usual
• Python -- the usual
• Ruby -- has a convention thats pretty neat
  (youll see an example later)
• Ending in ?, returns true or false
• Ending in !, in place modifier of the object
  itself
• Ending in , a setter of an instance variable

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Arrays

• Arrays can change size dynamically.
• Elements can be of different types
• Can do the standard indexing and slicing
  operations.
• Javascript example (next slide)
• All three let you use negative indexes to offset
  from the end

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Javascript - simple array

• // see array.html
• var arr1 2, 4, 6, 8, "who", "do", 'we',
  "appreciate", "?"
• document.write("Outputting initialized arr1
  ")
• document.write(arr1)
• document.write("I'm slicing the arr1
• from index 2 to 3nd from end")
• arr2 arr1.slice(2, -2)
• document.write(arr2)
• document.write("I'm adding elements to arr1
  
• at index 20, 21")
• arr120 1, 2, 3
• arr121 "ta"
• document.write(arr1)

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Dictionary

• JavaScript Arrays can be Associate Arrays (like
  property lists) - see assoc-array.html
• arr1"dog" "mammal"
• arr1"parrot" "bird"
• arr1"tarantula" "arachnid"
• for (var i in arr1)
• document.write(arr1i " ")
• Python and Ruby use a different data structure
• Python next slide

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Dictionary

• Python example (from idle)
• dict "dog" "mammal", "cat" "mammal",
  (10, 'a') 42
• dict
• (10, 'a') 42, 'dog' 'mammal', 'cat'
  'mammal'
• str(dict)
• "(10, 'a') 42, 'dog' 'mammal', 'cat'
  'mammal'"
• dict.keys()
• (10, 'a'), 'dog', 'cat'
• dict.values()
• 42, 'mammal', 'mammal'
• dict(10, "a")
• 42

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Composite types Summary for Python
Each type has many useful methods indexing and
slicing are essentially the same for all types

• String, immutable, a sequence of character this
  is a string
• String delimiters are , ,
• List, mutable, a sequence of anything ( 3, 4,
  abc)
• Array, similar to Javas ArrayList
• this, 1, -4.2, 4, abc
• Can insert and delete to a list. Many methods
  available
• y .append(twenty) y has value twenty
• Tuple, an immutable set of items
• (smith, jane, 24000, 123-45-6789)
• Dictionary, a property list or hash table. The
  key is immutable
• (smith, jane, 24000, 123-45-6789) 4,
  vehicle truck, age 19

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Defining Methods

• Javascript and Python have an explicit return
  statement, that may be ignored by the caller
• Ruby always returns the last value computed (may
  be ignored by caller)
• All allow for variable argument lists
• Python allows for naming parameters

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Closures

• All three allow for some kind of closure (an
  unnamed function)
• Ruby example coming up later in looping

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Control Structures

• The usual suspects with differences in syntax
  IF, Looping (while, for, etc), Switch, break,
  continue.
• Ruby is a little richer with unless (opposite of
  if) and until (opposite of while).

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Event handling

• All offer event handling with variations in syntax

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Ruby expressiveness looping examples (1)
fitz56.rb initialize array values 1, 2,
"buckle", "my", "shoe" puts "\n--print array
using while" i 0 while i 'do' is optional here print valuesi, " " i
1 end puts "\n\n-- using 'do-while'" i0 begin
print valuesi, " " i 1 end while i values.size
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Ruby expressiveness looping examples (2)
puts "\n\n--print array using nameless
function" values.each do e print e, "
" end puts "\n\n--print array using nameless
function with " values.each e print e, " "
puts "\n\n--print array using for" for i in
0..values.size-1 do print valuesi, "
" end puts "\n\n--using Integer's upto
method" 0.upto(values.size-1) i print
valuesi, " "
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Creating classes - Many similarities

• Class definitions are open, so instance variables
  and members can be added later, methods can be
  overridden by adding the new definition.
• Single inheritance. Object is the base class.

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JavaScript class example defining

• // see objects.html
• function Horse (name)
• this.name name
• this.getName getHorseName
• this.setName setHorseName
• function getHorseName ()
• return this.name
• function setHorseName(name)
• this.name name

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JavaScript class example modifying

• Horse.prototype.gait "walk"
• function getHorseGait ()
• return this.gait
• function setHorseGait (gait)
• this.gait gait
• Horse.prototype.setGait setHorseGait
• Horse.prototype.getGait getHorseGait

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Ruby class example Defining

• fitz128.rb
• class Horse def initialize (name) execute
  AFTER instantiation _at_name name instance
  variable end def name getter _at_name
  end last value is returned def name
  (name) setter _at_name name endend

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Ruby class example modifying

• fitz128b.rb
• repeated code deleted
• class Horse
• def initialize ( name 'pokey', age 10)
• _at_name name
• _at_age age
• end
• def say_whoa
• puts "Whoa there " _at_name
• end
• end

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Python class example defining
Run in IDLE

• Class Doggie
• size 25
• friendly True
• def sayArf(self)
• print(arf)
• fifi Doggie()
• fifi.size
• fifi.sayArf()

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Ruby metaprogramming to make class definition
easier

• To irb
• class Horse
• attr gait, true
• attr name, true
• def say_whoa
• puts Whoa there _at_name
• end
• end
• Horse.instance_methods - Object.instance_methods
• h1 Horse.new
• h1.name pokey
• h1.gait trot
• p h1

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Python code Example 1 defining a function
def fib(n) Calculate
fibonacci Number of parameter if n 1 return 1 else return n
fib(n-1)
fib
type(fib) help(fib) help on
function fib in module __main__ fib(n)
calculate fibonacci number of parameter
fib(5) 120
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Python code Example 2 A couple stacks
p type(p)
p.append(1) p.append(2)
p.append(buckle) p.append(my)
p.append(5) p 1, 2, buckle, my, 5 q
while p q.append(p.pop())
p q 5, my, buckle, 2, 1
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Python list mapping
li range(10) li 0, 1, 2, 3, 4, 5, 6,
7, 8, 9 li2 i2 for i in li li2 0,
2, 4, 6, 8, 10, 12, 14, 16, 18 li 0, 1, 2,
3, 4, 5, 6, 7, 8, 9
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Documentation

• JavaScript ?
• Python
• help( . . .) returns the docstring of the object
• Ruby
• ri, shell command

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At the end of the day

• Everyone should make a language
• Many similarities between JavaScript, Python and
  Ruby
• dynamic typing
• OO
• Single inheritance
• Flexible list lengths
• Interesting (useful) data types list, hash,
  tuple,
• Lambdas, closures
• Modifiable class definitions

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Which is better? Javascript?

• Javascript feels kind of klugey -- especially in
  its OO support, but also in some other things
  (e.g. the same variable can hold an indexed array
  and a dictionary)
• Javascript is quite accessible, especially to
  old-school computer profs who learned to
  program in a procedural language.
• The close connection with client-side programming
  has affected the typical development environment
  in unpleasant ways (because, mostly, of
  non-standard compliant browsers).
• Debugging support is not good.
• Still the go-to language for dynamic web pages
• There are lots of Javascript libraries out there.
  You have to find what you want and include it
  with

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Which is better? Python?

• Easy learning curve for the initial bit.
• Great for quick development
• Very readable code, thanks to the indent rule and
  other syntax rules
• OO is pretty good -- cleaner than JavaScripts
• Lovely set of data types
• My opinion I found the syntax very natural
• Code is not too terse good for noobs to read
  write.
• Import is easy
• Very easy to get information from interpreter
• Really nice debugging support, both in terms of
  debugger and in terms of online help
• I had an easier time moving between the IDE and
  the shell with Python than with Ruby
• Terrific community and support.

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http//imgs.xkcd.com/comics/python.png
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Which is better? Ruby?

• OMG! If I were a CS senior, this is the language
  I would code in. It is a programmers language.
  Like perl (with a scheme-feel for OO, and some
  lisp thrown in) but with a lot more stuff and
  slightly more disciplined.
• Very pristine OO framework.
• Very easy to get information from interpreter --
  most powerful support for reflection.
• As a teacher, no way! Other peoples code is
  already hard enough to read.
• Development environment is not as strong as
  Pythons.
• An enthusiastic and growing fan-base.
• POLS, principle of least surprise (the language
  should minimize confusion for experienced users).
• Ruby-on-Rails is reputed to be a killer app

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Downloads?

• Javascript is typically available with a browser.
  Develop in a plain text editor and execute in the
  browser.
• Python and Ruby both come with Linux/Unix
  distributions -- so hurrah for OSX.
• Python and Ruby interpreters have been
  implemented for assorted platforms, including
  Windows.

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Resources

• Javascript
• About a gazillion Web tutorials
• JavaScript Standard (OReilly book)
• Many, many, many crappy textbooks and how-to
  books. Run away!
• Python www.python.org
• Guidos tutorial is very good.
• The online book, Dive into Python is good for
  programmers
• Python for Dummies. 2 stars.
• Ruby www.ruby-lang.org
• There are some tutorials there. Not bad.
• I can recommend Fitzgeralds Learning Ruby
  (OReilly). Very simple and readable.

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EOTQuestions?