CSC/ECE 517 Fall 2009/wiki1a 11 f1,

Ruby and Python are both scripting languages whose popularity has sky rocketed in recent years. Both languages are High-Level, Garbage-collected, and Dynamically-typed. Both provide an interactive shell, standard libraries, and persistence support. So, what are the differences?

Points of comparison:

• Language Features
• Web programming environments
• Features exclusive to each
• Advantages of each over statically typed languages
• Project environments suited to each

Language Features

Access levels for methods and instance variables

One of the differences of Ruby compared to Python and Perl is that Ruby keeps all of its instance variables completely private to the class and only exposes them through accessor methods (attr_writer, attr_reader, etc).

Python's property descriptors are similar, but come with a tradeoff in the development process. If one begins in Python by using a publicly exposed instance variable and later changes the implementation to use a private instance variable exposed through a property descriptor, code internal to the class may need to be adjusted to use the private variable rather than the public property. Ruby removes this design decision by forcing all instance variables to be private, but also provides a simple way to declare set and get methods.

To make methods and instance variables private in Python, one always needs to write __ in front of the name. In Ruby, instance variables are private by default. Methods defined after the method call private are private.

Functions and methods

In Ruby, the part which is different from Python is the fact that all operations are messages to objects. There are no separate functions and methods; all of them are methods.

string = 'Hello world'
puts string.count('o'), string.length  # prints 2, 11

In Python, there are separate methods and functions as shown in the example below.

string = 'Hello world'
print string.count('o'), len(string)  # prints 2, 11 – why not string.len()?

Ruby has reference to class in class body

Ruby:

class MyClass
    initialize_magick()
end

Rubys variant is cleaner, as the magic stuff is done in the class definition, so you see that it’s being done when you look at the class.

Python:

class MyClass:
    pass
initialize_magick(MyClass)

But it’s really not a big deal, because calling the initialise method after the class or as a decorator is really not a major drawback.

First parameter of method definition

In Python, one needs to write self as the first parameter of a method definition (alike Perl). Furthermore, Python doesn’t require the variable name to be self. In Ruby, self is automatically available in a similar fashion as in C++.

Additionally, the method call self.method can be shortened to method, as self is the default receiver.

Ruby continuations vs Python Generators

Continuation is a "pointer" to the current position in your program, including calling stack and all variables. You can reuse that pointer to "go back in time" when needed. Continuations are useful when it comes to usecases.

def loop
  cont=nil
  for i in 1..4
    puts i
    callcc {|continuation| cont=continuation} if i==2
  end
  return cont
end

Python doesn't support full continuations or even coroutines; instead it supports "generator" functions which create a kind of limited coroutine. A generator in python is implemented as a special syntax for creating an instance of an iterator object, which returns the values returned by the "function" definition you provide. Python generators are easy and clean. The equivalent code for the above code segment, in python is

from generator_tools import copy_generator

def _callg(generator, generator_copy=None):
    for _ in generator: # run to the end
        pass
    if generator_copy is not None:
        return lambda: _callg(copy_generator(generator_copy))

def loop(c):
    c.next() # advance to yield's expression
    return _callg(c, copy_generator(c))

if __name__ == '__main__':
    def loop_gen():
        i = 1
        while i <= 4:
            print i
            if i == 2:
                yield
            i += 1

    c = loop(loop_gen())
    print("c:", c)
    for _ in range(2):
        print("c():", c())

Indentation

Python uses whitespace indentation, rather than curly braces or keywords, to delimit statement blocks (a feature also known as the off-side rule). An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block. On the other hand, ruby doesn't need any indentation although it can be optionally used for clarity.