[perl-python] 20050124 classes & objects

Xah Lee xah at xahlee.org
Mon Jan 24 09:54:16 EST 2005

© # -*- coding: utf-8 -*-
© # Python
© # in Python, one can define a boxed set
© # of data and functions, which are
© # traditionally known as "class".
© # in the following, we define a set of data
© # and functions as a class, and name it xxx
© class xxx:
©     "a class extempore! (^_^)"
©     i=1 # i'm a piece of data
©     def okaydokey(self): return "okaydokey"
©     def square(self,a): return a**a
© # in the following,
© # we create an object, of the class xxx.
© # also known as "instantiate a class".
© x = xxx()
© # data or functions defined in a class
© # are called the class's attributes or
© # methods.
© # to use them, append a dot and
© # their name after the object's name.
© print 'value of attribute i is:', x.i
© print "3 squared is:", x.square(3)
© print "okaydokey called:", x.okaydokey()
© # in the definition of function inside a
© # class, the first parameter "self" is
© # necessary. (you'll know why when you need to)
© # the first line in the class definition
© # is the class's documentation. It can
© # be accessed thru the __doc__
© # attribute.
© print "xxx's doc string is:", x.__doc__
© # one can change data inside the class
© x.i = 400
© # one can also add new data to the class
© x.j=4
© print x.j
© # or even override a method
© x.square = 333
© # (the following line will no longer work)
© # print "3 squared is:", x.square(3)
© # in Python, one must be careful not to
© # overwrite data or methods defined in a
© # class.


for a obfuscated treatment with a few
extra info, see

in Python terminal, type help() then
topic CLASSES to read about existing
datatypes as classes, and classes in

try to write a class with one data of
integer and two functions, one
increases it by 1, one decreases it by
1.  note: inside a class definition,
to refer to data inside itself use
self. e.g. self.i

Perl does not support classes or
objects in the so-called "Object
Oriented" programing. However, a
complete set of emulations of OO
style of programing have been done,
resulting in modules and books and
many documentations and tutorials.

here is a quote from
perldoc perlobj

First you need to understand what
references are in Perl. See perlref for
that. Second, if you still find the
following reference work too
complicated, a tutorial on
object-oriented programming in Perl can
be found in perltoot and perltooc.

it goes on and sayz:

If you're still with us, then here are
three very simple definitions that you
should find reassuring.

1.  An object is simply a reference
that happens to know which class
it belongs to.

2.  A class is simply a package that
happens to provide methods to deal
with object references.

3.  A method is simply a subroutine
that expects an object reference
(or a package name, for class
methods) as the first argument.

Good luck.

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if you are reading it on a web page, program examples may not run
because html conversion often breaks the code.
 xah at xahlee.org

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