Young & Interpreted: Python, Ruby, JavaScript

1. Young & Interpreted:Python, Ruby, JavaScript Susan Haynes 18 February 2008

2. 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 ---> it’s a duck. • Interpreted -- Source code is not compiled then executed. Instead, the source is executed by the interpreter • Released ‘92 - ‘95

3. They’re 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.

4. 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’

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

6. What do I know? • Not much. I haven’t 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).

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

8. 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.

9. 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.

10. 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

11. Variable Names • JavaScript -- the usual • Python -- the usual • Ruby -- • Local variables start with lower case or _ • Instance variables start with @ • Class variables start with @@ • Globals start with $

12. Simple Python Program Output enter integer: 3 enter float: -14.34 s1+s2 3-14.34 n1+n2 -11.34 First program: first.py s1 = raw_input(“enter integer: “) s2 = raw_input(“enter float: “) s3 = s1 + s2 print “s1+s2 “ + s3 + “\n” n1 = int(s1) n2 = float(s2) n3 = n1+n2 print “n1+n2: “ + n3 Run this with Python and Idle import first then reload(first) on subsequent changes

13. 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): <type ‘int’> type(y): <type ‘str’> type(y): <type ‘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

14. Parallel Assignment Python, Ruby and JavaScript 1.7 have parallel assignments. Here is a python example (idle) >>> t = (‘a’, ‘b’, ‘c’) >>> type(t) <type ‘tuple’> >>> t[0] ‘a’ >>> t[1] ‘b’ >>> type ( (x, y, z) ) <type ‘tuple’> >>> (x, y, z) = t >>> x ‘a’ >>> y ‘b’

15. Method Names • JavaScript -- the usual • Python -- the usual • Ruby -- has a convention that’s pretty neat (you’ll 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

16. 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

17. Javascript - simple array // see array.html var arr1 = [2, 4, 6, 8, "who", "do", 'we', "appreciate", "?" ]; document.write("<h2>Outputting initialized arr1 “ + “</h2>"); document.write(arr1); document.write("<h2>I'm slicing the arr1 “ + “from index 2 to 3nd from end</h2>"); arr2 = arr1.slice(2, -2); document.write(arr2); document.write("<h2>I'm adding elements to arr1 “ + at index 20, 21</h2>"); arr1[20] = [1, 2, 3]; arr1[21] = "ta"; document.write(arr1);

18. 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(arr1[i] + " "); • Python and Ruby use a different data structure • Python: next slide

19. 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

20. 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 Java’s 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 }

21. 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

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

23. 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).

24. Event handling All offer event handling with variations in syntax

25. 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 < values.size do # 'do' is optional here print values[i], " " i += 1 end puts "\n\n--> using 'do-while'" i=0 begin print values[i], " " i += 1 end while i < values.size

26. 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 values[i], " " end puts "\n\n-->using Integer's upto method" 0.upto(values.size-1) { |i| print values[i], " " }

27. 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.

28. 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 }

29. 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;

30. Ruby class example: Defining # fitz128.rb class Horse def initialize (name) # execute AFTER instantiation @name = name # instance variable end def name # getter @name end # last value is returned def name= (name) # setter @name = name endend

31. Ruby class example: modifying #fitz128b.rb # repeated code deleted class Horse def initialize ( name = 'pokey', age = 10) @name = name @age = age end def say_whoa puts "Whoa there " + @name end end

32. Run in IDLE Python class example: defining Class Doggie: size = 25 friendly = True def sayArf(self): print(“arf”) fifi = Doggie() fifi.size fifi.sayArf()

33. To irb class Horse attr :gait, true attr :name, true def say_whoa puts “Whoa there “ + @name end end Horse.instance_methods - Object.instance_methods h1 = Horse.new h1.name= “pokey” h1.gait = “trot” p h1 Ruby: metaprogramming to make class definition easier

34. 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 <function fib at 0xc3d3b0> >>> type(fib) <type ‘function’> >>> help(fib) help on function fib in module __main__: fib(n) calculate fibonacci number of parameter >>> fib(5) 120

35. Python code Example 2: A couple stacks >>> p = [] >>> type(p) <type ‘list’> >>> 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]

36. Python list mapping >>> li = range(10) >>> li [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> li2 = [i*2 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]

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

38. 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

39. 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 <script type=“text/javascript” src=“library.js” />

40. 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 JavaScript’s • 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.

41. http://imgs.xkcd.com/comics/python.png

42. Which is better? Ruby? • OMG! If I were a CS senior, this is the language I would code in. It is a programmer’s 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 people’s code is already hard enough to read. • Development environment is not as strong as Python’s. • 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”

43. 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.

44. Resources • Javascript • About a gazillion Web tutorials • JavaScript Standard (O’Reilly book) • Many, many, many crappy textbooks and how-to books. Run away! • Python www.python.org • Guido’s 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 Fitzgerald’s Learning Ruby (O’Reilly). Very simple and readable.

45. EOTQuestions?