[Tutor] defining __init__

[Danny Yoo]

On Thu, 12 Jan 2006, Christopher Spears wrote:

> I just read about __init__ in the chapter on operator
> overloading in Learning Python.  What is __init__
> exactly?  Is it a special function that you can use to
> initialize attributes in an object upon creation?

Hi Chris,

Yes, that's it.

__init__'s doesn't have to do with overloading, but does have to do with
initialization.  It fires off when an instance is being instantiated.

For example:

######
class Dog:
    def __init__(self, name):
        self.name = name

    def bark(self):
        return "%s says 'bow wow'" % self.name
######


When we instantiate a Dog, we pass parameters that will be used to call
__init__, and in effect, we "initialize" our dog:


###
>>> d = Dog("Ein")
>>> d.bark()
"Ein says 'bow wow'"
>>> k = Dog("Kujo")
>>> k.bark()
"Kujo says 'bow wow'"
>>> Dog()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: __init__() takes exactly 2 arguments (1 given)
###

Note that in the third call to Dog, we see that if we don't pass enough
arguments, that __init__() won't fire off properly.


Does this make sense?