Core Python Programming, Second Edition (Pamela Gallagher's Library) by Wesley J. Chun

Author:Wesley J. Chun
Language: eng
Format: epub
Publisher: Prentice Hall
Published: 2007-06-14T16:00:00+00:00

When the class is invoked, the first step in the instantiation process is to create the instance object. Once the object is available, Python checks if an __init__() method has been implemented. By default, no special actions are enacted on the instance without the definition of (or the overriding) of the special method __init__(). Any special action desired requires the programmer to implement __init__(), overriding its default behavior. If __init__() has not been implemented, the object is then returned and the instantiation process is complete.

However, if __init__() has been implemented, then that special method is invoked and the instance object passed in as the first argument (self), just like a standard method call. Any arguments passed to the class invocation call are passed on to __init__(). You can practically envision the call to create the instance as a call to the constructor.

In summary, (a) you do not call new to create an instance, and you do not define a constructor: Python creates the object for you; and (b) __init__(), is simply the first method that is called after the interpreter creates an instance for you in case you want to prep the object a little bit more before putting it to use.

__init__() is one of many special methods that can be defined for classes. Some of these special methods are predefined with inaction as their default behavior, such as __init__(), and must be overridden for customization while others should be implemented on an as-needed basis. We will cover many more of these special methods throughout this chapter. You will find use of __init__() everywhere, so we will not present an example here.

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