Young & Interpreted:Python, Ruby, JavaScript

Susan Haynes18 February 2008

Susan Haynes18 February 2008

These three languages have a lot in common: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

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

They’re Really DifferentThey’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.

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.

OriginsOrigins

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’

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’

QuestionsQuestions

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

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

What do I know?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).

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).

DemosDemos

JavaScript using browser :-( Python using IDLE or shell (python file)

Ruby using irb or shell (ruby file.rb)

JavaScript using browser :-( Python using IDLE or shell (python file)

Ruby using irb or shell (ruby file.rb)

White SpaceWhite 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.

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.

Line terminationLine 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.

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.

NumbersNumbers

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 true3.class ==> return Fixnum3.to_f ==> returns 3.0

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 true3.class ==> return Fixnum3.to_f ==> returns 3.0

Variable NamesVariable 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 $

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 $

Simple Python ProgramSimple Python Program

First program: first.pys1 = raw_input(“enter integer: “)s2 = raw_input(“enter float: “)s3 = s1 + s2print “s1+s2 “ + s3 + “\n”n1 = int(s1)n2 = float(s2)n3 = n1+n2print “n1+n2: “ + n3

Outputenter integer: 3enter float: -14.34s1+s2 3-14.34

n1+n2 -11.34

Run this with Python and Idleimport firstthen reload(first) on subsequent changes

Another simple Python programAnother simple Python program

Second program: second.py

x = 10y = ‘3’print “type(x): “ , type(x)print “type(y): “, type(y)y = int(y)print “type(y): “, type(y)dir()

Output

>>> import secondtype(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 varXstr(varY): any varY has a “nice” string representationdir(): lists all known names

Parallel AssignmentParallel Assignment

Python, Ruby and JavaScript 1.7 have parallel assignments.

Here is a python example (idle)

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’

Method NamesMethod 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

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

ArraysArrays

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

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

Javascript - simple arrayJavascript - simple array// see array.htmlvar 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);

// see array.htmlvar 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);

DictionaryDictionary

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

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

DictionaryDictionary

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

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

Composite types Summary for PythonComposite types Summary for Python

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 }

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 }

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

Defining MethodsDefining 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

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

ClosuresClosures

All three allow for some kind of closure (an unnamed function)

Ruby example coming up later in looping

All three allow for some kind of closure (an unnamed function)

Ruby example coming up later in looping

Control StructuresControl 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).

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).

Event handlingEvent handling

All offer event handling with variations in syntax

All offer event handling with variations in syntax

Ruby expressiveness: looping examples (1)Ruby expressiveness: looping examples (1)

# fitz56.rb#initialize arrayvalues = [1, 2, "buckle", "my", "shoe"]

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

Ruby expressiveness: looping examples (2)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], " " }

Creating classes - Many similarities

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.

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.

JavaScript class example: defining

JavaScript class example: defining

// see objects.htmlfunction Horse (name) { this.name = name; this.getName = getHorseName; this.setName = setHorseName; } function getHorseName () { return this.name; } function setHorseName(name) {

this.name = name}

// see objects.htmlfunction Horse (name) { this.name = name; this.getName = getHorseName; this.setName = setHorseName; } function getHorseName () { return this.name; } function setHorseName(name) {

this.name = name}

JavaScript class example: modifying

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;

Horse.prototype.gait = "walk";

function getHorseGait () {

return this.gait;

}

function setHorseGait (gait) {

this.gait = gait;

}

Horse.prototype.setGait = setHorseGait;

Horse.prototype.getGait = getHorseGait;

Ruby class example: DefiningRuby 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

# 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

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

#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

Python class example: defining

Class Doggie:

size = 25

friendly = True

def sayArf(self):

print(“arf”)

fifi = Doggie()

fifi.size

fifi.sayArf()

Class Doggie:

size = 25

friendly = True

def sayArf(self):

print(“arf”)

fifi = Doggie()

fifi.size

fifi.sayArf()

Run in IDLE

Ruby: metaprogramming to make class definition

easier

Ruby: metaprogramming to make class definition

easierTo irbclass Horse attr :gait, true attr :name, true def say_whoa puts “Whoa there “ + @name endend

Horse.instance_methods - Object.instance_methodsh1 = Horse.newh1.name= “pokey”h1.gait = “trot”p h1

To irbclass Horse attr :gait, true attr :name, true def say_whoa puts “Whoa there “ + @name endend

Horse.instance_methods - Object.instance_methodsh1 = Horse.newh1.name= “pokey”h1.gait = “trot”p h1

Python code Example 1: defining a function

Python code Example 1: defining a function

>>> def fib(n): “””Calculate fibonacciNumber 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

Python code Example 2: A couple stacks

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]

Python list mappingPython 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]

DocumentationDocumentation

JavaScript ? Python

help( . . .) returns the docstring of the object

Ruby ri, shell command

JavaScript ? Python

help( . . .) returns the docstring of the object

Ruby ri, shell command

At the end of the dayAt 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

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

Which is better? Javascript?

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” />

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” />

Which is better? Python?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.

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.

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

Which is better? Ruby?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”

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”

Downloads?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.

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.

ResourcesResources 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.

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.

EOTQuestions?

EOTQuestions?