ruby_vs_perl_and_python

Comparing and introducing Ruby
Michael Neumann
5. February 2000

1

c Copyright 2000 Michael Neumann

The distribution of this document in electonical or printed form is allowed, as
long as it’s content including the author and copyright notices remain unchanged
and the distribution take place for free apart from a fee for the data carrier disk,
the copy process etc.

If questions occur or you discover errors or if you have improvement suggestions
you can write me an email: <neumann@s-direktnet.de>.

3

Informations about Ruby and the Ruby interpreter as well as many libraries
are availabe from the official Ruby-Homepage: http://www.ruby-lang.org.

I’ll compare Ruby with Perl and Python, because I think they are the most
frequently used and best known ones. Ruby has so much advantages against
Perl and Python, that I’ll try to mention here as much as possible.
At first I’ll shortly explain what Ruby is:
Ruby is a modern, interpreted and object-orientated programming language.
It has many similarities with Smalltalk (”everything is an object”, simple in-
heritance, metaclass-model, code-blocks, garbage-collector, typeless variables,
etc. . . ), but takes much of the well formed syntax of Eiffel (or who don’t know
that great language, it’s a little bit like Modula or Ada). Additionally many
useful elements from Perl were added (e. g. regular expressions, text-processing,
text-substitution, iterators, variables like $ $/ . . . ). Therefore, Ruby is a very
good alternative to Perl and Python. The difference between Perl and Ruby
is the much easier and better to understand syntax and the easy-to-use ”real”
object-orientation. Following term which I have found on a Ruby-page expresses
the power of Ruby:

Ruby > (Smalltalk + Perl) / 2

Some time ago I asked the author of Ruby, Yukihiro Matsumoto (aka matz),
about the history of Ruby and why he developed a new language. Here is his
original answer:

”Well, Ruby was born in Feb. 23 1993. At that day, I was talking
with my colleague about the possibility of object-oriented scripting
language. I knew Perl (Perl4, not Perl5), but I didn’t like it really,
because it had smell of toy language (it still has). The object-oriented
scripting language seemed very promising.
I knew Python then. But I didn’t like it, because I didn’t think it
was a true object-oriented language. OO features are appeared to
be add-on to the language. I, as a language mania and OO fan for
15 years, really really wanted a genuine object-oriented, easy-to-use
object-oriented scripting language. I looked for, but couldn’t find one.
So, I decided to make it. It took several months to make the inter-
preter run. I put it the features I love to have in my language, such
as iterators, exception handling, garbage collection.
Then, I reorganized the features in Perl into class library, and im-
plemented them. I posted Ruby 0.95 to the Japanese domestic news-
groups in Dec. 1995.
Since then, mail lists are established, web pages are formed. Highly
active discussion was held in the mail lists. The oldest list ruby-list
has 14789 messages until now.
Ruby 1.0 was released in Dec. 1996, 1.1 in Aug. 1997, 1.2 (stable
version) and 1.3 (development version) were released in Dec. 1998.
Next stable version 1.4 will be shipped this months (June 1999), hope-
fully.”

4

As you can see, Ruby was developed, having Perl, Python, Smalltalk and
Eiffel (as well as some other languages) in mind. So matz took the best from
the above called languages to make a new, better, object-orientated scripting-
language. Unlike Perl and Python Ruby was designed totally object-orientated
right from the beginning. So there’s no clumsy syntax for declaring a class like
in Perl. That is why many people, myself included, say that Perl isn’t really
object-oriented. I agree with Stroustrup, the developer of C++, who once said
that a special programming-style (e. g. OOP) is only sufficient supported if the
language makes it easy to use this one. And I do not think that Perl supports
sufficient enough the use of the object-oriented paradigm.
A big advantage of Ruby is, that it is very easy to learn, and so could perhaps
become a language to introduce people into programming or object-orientation
(maybe at school instead of the often used language Pascal). It took me only one
day to get into Ruby and after some weeks I was nearly an expert! For learning
Python it took me a little bit longer, but for learning Perl you normally need
months and to become an expert even years. The syntax of Ruby is IMHO so
easy that even non-Rubyists can read and understand most of the sourcecode,
if it is written in clean Ruby and not Perl-like.
A good tutorial is very important when starting to learn a new language.
Therefore big thanks to matz and the translators of Ruby User’s Guide 1 , which
is a short but almost everything covering introduction into Ruby. Also the Ruby
Language Reference Manual 2 is very good. Looking at the tutorials of Python
and Perl I have noticed following: either they are very long or they do not cover
all aspects (especially Perl).
As already mentioned above, the syntax of Ruby is very easy, i. e. it is very
clean, readable but also short. The code nearly documents itself, like in Eiffel
and unlike Perl, which is the opposite. Clean, understandable and short code
increases productivity, because it increases the speed of coding, reduces the
need of documenting, is less error-prone and therefore it is easier to maintain.
In Perl, very much time is wasted in finding errors or to document code. Even
some errors are first detected after some time. In Ruby you have the possibility
to make your code much more readable by inserting additionally keywords or
by using words instead of operators. Now a small example of doing one and the
same task in different styles in Ruby:

# short form
(1..10).each { |i|
print "#{i}n" if i % 2 == 0 && i > 5
}

# the same more readable
(1..10).each do |i|
if i % 2 == 0 and i > 5
print i, "n"
end
end

# the same more readable, with syntax-sugar for (1..10).each
1 http://www.math.sci.hokudai.ac.jp/%7Egotoken/ruby/ruby-uguide
2 http://hydrogen.ruby-lang.org/en/man-1.4

5

for i in 1..10 do
if i % 2 == 0 and i > 5 then
print i, "n"
end
end
In Perl you would write:
for (1..10) {
if($_ % 2 == 0 && $_ > 5) {
print "$_n";
}
}
And in Python:
for i in range(1,11):
if(i % 2 == 0 and i > 5): print i,"n"
The .. operator in Ruby creates an Range-object. You can take every object
which is comparable with the <=> operator and which have the succ-method.
So you can also iterate over a string-range (e. g. "a".."ab"). In Python you
need the function range to create an array over which you can then iterate. In
Ruby you can choose between the keywords and, or, not and the operators &&,
||, !. The keyword then is optional and you can choose between {. . . } and do
. . . end.
Semicolons are only necessary if you want to write more than one statement
into one line. This is like Python but unlike Perl, where you have to end every
statement with a semicolon, which has only disadvantages, e. g. it result in more
errors, because you often forget them, and make code less readable.
Another disadvantage of Perl is, that it diﬀerentiates between scalar (e. g.
string, integer, reference) and non-scalar (e. g. array, hash) variables which
makes programming much more diﬃcult. A problem appears, when you want
to create an array which itself contains arrays, because arrays or hashs in Perl
can only contain scalar values. The solution is to put the references of the arrays
into the array. But that’s not easy and you can make many faults. Not so in
Ruby and Python, where variables only contain references to objects.
An advantage of Ruby is, that all constructs have a value. For example an
if-construct returns a value, so you can use if also on the right side of an
expression. The following example shows this:
txt = "Hello World"

a = "size " +
if txt.size > 3 then
"greater"
else
"less"
end +
" than 3"

print a # prints "size greater than 3"

6

Functions in Perl do not automatically introduce a new scope, so if you use a
variable, which was already declared outside the function, it will be overwritten.
You need ’my’ or ’local’ to declare local variables. Ruby let you easily create
constants (begins with a capital letter), local variables (begins with a small
letter), global variables (begins with a $) and instance variables (begins with a
@).

But the most important aspect, why I am using Ruby instead of Python or
Perl are the object-orientated features of Ruby, and that Ruby was designed
object-oriented right from beginning, unlike Python and Perl where object-
orientation was added on later. You can recognize this in e. g. in Python very
good, because the ﬁrst parameter (often named self) of every method of a class
is the object on which the method is called:
class A:
def method_a (self):
# do what you want

The syntax of declaring a class in Ruby couldn’t be easier:
class X
...
end
Now you see how a class in Perl is declared:
sub new {
my ($class,@args) = @_;
bless({@args}, $class);
}
You see, Ruby is much more intuitive. Now an example of declaring a Point-
class in Ruby:
class Point

# initialize is called implicit when Point.new is called
def initialize (x, y)
@x = x # @x is an instance variable
@y = y # @y is an instance variable
end

# returns x (because instance variables are only
# visible inside the class)
def x
@x # the same as return @x
end

# the same like ’def x’
def y; @y end

# the setter-function

7

def x= (x)
@x = x
end

def y= (y)
@y = y
end

end
To make the code shorter and better to read, the same class using the attr accessor-
function of module Module, which dynamically creates a getter- and setter-
method for each parameter is shown:
class Point
attr_accessor :x, :y

@x = x
@y = y
end
end

There are also some other useful methods, like attr reader, attr writer as
well as attr.
Ruby’s instance variables are only accessible from inside the class, you cannot
change this. This is advanced object-orientation. You’ll see this in Eiﬀel as well
as in Java but not in Python, where you can access the variables from outside
the class. For example JavaBeans use method-names like get varname and
set varname to access instance variables (where varname is the name of the
variable). These are also called attributes. But Ruby has the ability to access
the instance-variables through methods as if they were directly assigned. Here
an example of using the Point-class:

a = Point.new (1,6) # create object "a" of class Point

a.x = 5 # calls the method x= with the paramter 5
print a.x,"n" # prints 5
print a.y,"n" # prints 6

There’s no direct access to instance variables. But sometimes you want to use a
class the same way as in Python, where you can assign instance variables from
outside without declaration. A short example in Python:
# empty class
class A:
pass

x = A() # create object "x" of class A

x.a = 3 # create new instance variable
print x.a # prints 3

8

The same behavior can be reached in Ruby by using the class OpenStruct
defined in file ostruct.rb. Now the same example like above in Ruby:
require ’ostruct’

x = OpenStruct.new # create object "x" of class OpenStruct

x.a = 3
print x.a # prints 3
There is almost no difference between the two example. But in Python you have
to declare an own class! This behavior is very easy to impemented in Ruby,
because Ruby calls the method method missing for every unknow method (in
this case this would be the method a=. So you can then dynamically create the
method a which returns the value 3.
Now we’ll extend the Point-class of an equality-operator. You do not need to
insert the ”==”-method into the above written Point-class, you can also extend
the existing Point-class in adding a whole Point-class (not recommended in this
case). The whole Point-class could now look like:

class Point

@x = x
@y = y
end
end

class Point
def == (aPoint)
aPoint.x == x and aPoint.y == y
end
end
or better like this:

class Point

@x = x
@y = y
end

def == (aPoint)
aPoint.x == x and aPoint.y == y
end

end

9

As you can see, Ruby is very easy and clean. But there are more features. In
Ruby there are some conventions which you should not break. Method names
which ends with:

• = should be used as setter of instance-variables
• ? should return a boolean (e. g. has key? of class Hash)

• ! signalize that data inside the object is changed and not the values which
is returned (e. g. downcase! which directly changes the objects value and
downcase which returns the downcased value)

Now we’ll extend the given Array-class which comes with Ruby for a missing
method count(val), which counts the occurence of val. We do not need to
change any given sourcecode or inherit a given class:
class Array
def count (val)
count = 0

# each iterates over every item and executes the block
# between ’do’ and ’end’.
# the actual element of the iteration is stored into ’i’
each do |i|
if i == val then count += 1 end
end
count # returns ’count’
end
end

# now every declared Array has the method count(val)

print [1, 5, 3, 5, 5].count (5) # prints 3

Sometimes it could happen, that you do not want to construct e. g. a Point-
object via Point.new but via Point.new cartesian. Ruby has not only classes
but also meta-classes, like Smalltalk, i. e. the class-deﬁnition is available during
runtime and could also be changed. In Ruby every class is an object constructed
from the class Class. There are instance methods and class methods. Instance
methods do not exist without objects. Class methods do exist without objects,
they exist as far as a class is created. Class methods are called on classes (e. g.
Point.new), instance methods on objects or instances (e. g. "hallo".length).
Now we will create a class methods new cartesion for the class Point:
class Point
def new_cartesian (x, y)
aPoint = new(x,y)
# here you can do what you want
return aPoint
end

10

# makes new_cartesian a class method
module_function :new_cartesian
end

# now you can instatiate a Point-object with new_cartesian:
a = Point.new_cartesian(1, 43)
The same can also be done this way:

class Point
def Point.new_cartesian (x, y)
aPoint = new(x,y)
# here you can do what you want
return aPoint
end
end
Now about iterators, they can be declared very easy:

# iterates n-times over the given block
def times (n)
while n > 0 do
yield n
n -= 1
end
end

times(5) {|i| print i," " }

Prints 5 4 3 2 1 onto the screen. Here’s a more advanced example of using
iterators:

include FileTest

FILE, DIRECTORY, DIRECTORY_UP = 0..2
PATH_SEP = "/"

#
# depth: -1 = recurse all
# yield: path, name, type
#
def scan_dir(path, depth=-1)
# remove PATH_SEP at the end if present
if path[-1].chr == PATH_SEP then path = path.chop end

Dir.foreach (path) do |i|
next if i =~ /^..?$/
if directory? (path+PATH_SEP+i) then
yield path, i, DIRECTORY
scan_dir (path+PATH_SEP+i, depth-1) do |a,b,c|
yield a,b,c
end unless depth==0

11

yield path, i, DIRECTORY_UP
elsif file? (path+PATH_SEP+i)
yield path, i, FILE
end
end
end

# prints all files in directory /home and subdirectories
scan_dir ("/home",-1) { |path, name, type|
print path, PATH_SEP, name, "n" if type==FILE
}

The iterator scan dir iterates over all files and subdirectories and calls the
given block with path, filename and type as parameter.
Using blocks with methods, you can program very flexible, because you can
extend the method from outside. Here an example of measuring the time to
execute of a piece of code:

def Time.measure
start = Time.times.utime
yield
Time.times.utime - start
end

# measures the time used by the loop between { and }
print Time.measure {
for i in 1..100 do a = 10 end
}

Or counting the number of lines in a file:

def get_num_lines (file)
# iterates over every line of "file"
IO.foreach(file){}

# $. returns the number of lines read since
# last explicit call of "close"
$.
end
print get_num_lines ("/home/michael/htdocs/index.html")

IO.foreach(path) is a short form for:

port = open(path)
begin
port.each_line {
...
}
ensure
port.close
end

12

So in any case the file will be closed. You need not explicitly open the file or
close it. Another important use of blocks is for synchronizing threads:
require "thread"

m = Mutex.new

a = Thread.start {
while true do
sleep 1
m.synchronize do print "an" end
end
}

b = Thread.start {
while true do
sleep 2
m.synchronize do print "bn" end
end
}

sleep 10

a.exit # kill thread
b.exit # kill thread
The Mutex-object makes sure that only one thread can call simultaneous it’s
method synchronize. In Java e. g. to reach the same effect, the new keyword
synchronize was introduced (in comparison to C++), but in Ruby this is done
with a block-construct, so you’re much more flexible, because you can extend
or change the semantics.
Socket are also very easy to program. Following code will connect to a
Whois-server and get information about a domain:
require ’socket’

def raw_whois (send_string, host)
s = TCPsocket.open(host, 43)
begin
s.write(send_string+"n")
return s.readlines.to_s
ensure
s.close
end
end

print raw_whois("page-store.de", "whois.ripe.net")
There is also a TCPserver-class in Ruby, which makes it much easier to build a
server. Following a multi-threaded echo-server is shown:
require ’socket’

13

require ’thread’

server = TCPserver.open(5050) # build server on port 5050

while true do # loop endless (until Ctrl-C)
new_sock = server.accept # wait for new connection
print new_sock, " acceptedn"

Thread.start do # new thread for connection
sock = new_sock
sock.each_line do |ln| # read line from socket
sock.print ln # put line back to socket
end
sock.close # close connection
print sock, " closedn"
end
end

The exception-model of Ruby is very close to the one of Eiﬀel, where you
have pre- and post-conditions. In Ruby you have only post-conditions (ensure)!
Now a presentation of the possibilities the exception-model of Ruby gives you:

begin
# do anything...

# raise an exception of type RuntimeError
raise "Error occured"

# raise an exception of user-defined class
raise MyError.new(1,"Error-Text")

rescue
# is called when an exception occures, you can
# access the exception-object through $!, the error-message
# is accessible through $!.message and the file and
# line-number where the exception occured is stored in $@

# solve problem...and retry the whole block
retry

# or re-raise exception
raise

# or raise new exception
raise "error..."

ensure
# is always called before the block
# surrounded by "begin" and "end" is left
end

14

Regular Expressions are used like in Perl. To extract the top-level domain
from a domain-name you can deﬁne following method:
def extract_tld (domain)
domain =~ /.([^.]+)$/
$1
end

print extract_tld ("www.coding-zone.de") # prints "de"
Most of the features of Perl’s regular expressions are also available in Ruby.
Database-access is also available in Ruby, but not all databases are yet
supported. Currently only MySQL, Msql, PostgreSQL, Interbase and Oracle
are available. A generalized database-access standard like ODBC, JDBC or
DBD/DBI (Perl) would be very nice. Following code-example shows, how to
print out a whole database-table with MySQL:
require ’mysql’

m = Mysql.new(host, user, passwd, db) # creates new Mysql-object

res = m.query("select * from table") # query the database

# gets all fieldnames of the query
fields = res.fetch_fields.filter {|f| f.name}

puts fields.join("t") # prints out all fieldnames

# each row is printed
res.each do |row| # row is an array of the columns
puts row.join("t")
end
In Ruby, you can very easiliy implement dynamic argument-type checking.
Following code implements this behavior:
class Object
def must( *args )
args.each do |c|
if c === self then return self end
end

raise TypeError,
"wrong arg type "#{type}" for required #{args.join(’/’)}"
end
end

# this method requires an Integer as argument
def print_integer( i )
i.must Integer

15

print i
end

# you can also allow more than one type
# "name2s" returns an String, but takes a String or an Integer
def name2s( arg )
arg.must String, Integer
case arg
when String then arg
when Integer then arg.id2name
end
end

# :Hello is an Integer representing the string "Hello"
print name2s(:Hello) # prints "Hello"
print name2s(" World") # prints " World"
print name2s([1,2,3]) # raises TypeError

Writing C/C++ extension for Ruby is very easy. You can do all in C what
is possible in Ruby. It is also possible to use the SWIG interface-generator for
Ruby, but using the ruby-functions directly is very easy. Following a C-program
which declares a module and one method:
// filename: str_func.c
#include "ruby.h"
#include <stdlib.h> // for malloc

//
// Function will add "add" to each character of string "str"
// and return the result. Function do not change "str"!
// "obj" is assigned the class/module-instance on which method is called
//
extern "C" VALUE add_string( VALUE obj, VALUE str, VALUE add )
{
int len, addval, i;
char *p, *sptr;
VALUE retval;

// checks parameter-types
// if type is wrong it raises an exception
Check_Type(str, T_STRING);
Check_Type(add, T_FIXNUM);

// length of string "str"
len = RSTRING(str)->len;

// convert FixNum to C-integer
addval = FIX2INT(add);

// alloc temorarily memory for new string

16

p = (char*) malloc(len+1);

// raise an exception if not enough memory available
if( !p )
rb_raise(rb_eRuntimeError, "couldn’t alloc enough memory for string");

// get pointer to string-data
sptr = RSTRING(str)->ptr;

// iterate over each character, and add "addval" to it
for(i=0; i<len; ++i) p[i] = sptr[i] + addval;
p[i] = 0;

// create Ruby-string which contains the C-string "p"
retval = rb_str_new2(p);

// free memory
free(p);

return retval;
}

//
// function is called, when module is loaded (e.g. through require ’str_func’)
//
extern "C" EXTERN void Init_str_func(void)
{
// declare new module
VALUE module = rb_define_module(String_Functions");

// declare module-function
rb_define_module_function(
module, // module
"add_string", // name of method in Ruby
(unsigned long (__cdecl *)(void)) add_string, // pointer to C-function
2 // number of arguments
);
}
When compiled this as dynamic load library or static into the Ruby-interpreter,
you can use the module in Ruby:
require ’str_func’

# should print "JgnnqYqtnf"
print String_Functions.add_string("HelloWorld", 2)

Inheritance is very easy:
class A

17

def method_a
print "A::method_a"
end
end

# class B inherits from A
class B < A
def method_b
print "B::method_b"
end

# extend "method_a"
def method_a
super # calls A::method_a
print "B::method_a"
end
end

a = A.new
b = B.new

a.method_a # prints "A::method_a"
b.method_a # prints "B::method_a"
b.method_b # prints "A::method_a" and "B::method_a"

# now we’ll dynamically change a method of object "b"
# this will not change the class B!
class << b
def method_a
print "B::method_a"
end
end

b.method_a # prints "B::method_a"

Multiple inheritance is supported through mix-in, where a class includes one
or more modules. For example Array is a class which inherits from Object
(like every class) and includes the module Enumerable. This works a bit like
the interfaces in Java, but with the diﬀerence that an interface in Java cannot
contain code. In Ruby every module can be included (with include module-
name) into a class. This is like the programming-language Sather (very close to
Eiﬀel) do it.

For those who came from Python to Ruby and want to use their programs
written in Python inside Ruby-scripts, Ruby/Python 3 is the solution. Here is a
simple example of using Ruby/Python:

require ’python’
require ’python/ftplib’
3 http://www.goto.info.waseda.ac.jp/˜fukusima/ruby/python/doc/index.html

18

# create new object of Python-class "FTP"
ftp = Py::Ftplib::FTP.new(’ftp.netlab.co.jp’)
ftp.login
ftp.cwd(’pub/lang/ruby’)
ftp.dir
ftp.quit
This example shows how to use the Python-module Ftplib inside Ruby. You
can do almost everything which is possible in Python with Ruby/Python in
Ruby.

ruby_vs_perl_and_python

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