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Python Constructor

A constructor is a special type of method (function) which is used to initialize the instance members of the class.

Constructors can be of two types.

  1. Parameterized Constructor
  2. Non-parameterized Constructor

Constructor definition is executed when we create the object of this class. Constructors also verify that there are enough resources for the object to perform any start-up task.


Creating the constructor in python

In python, the method __init__ simulates the constructor of the class. This method is called when the class is instantiated. We can pass any number of arguments at the time of creating the class object, depending upon __init__ definition. It is mostly used to initialize the class attributes. Every class must have a constructor, even if it simply relies on the default constructor.

Consider the following example to initialize the Employee class attributes.

Example

Output:

ID: 101 
Name: John
ID: 102 
Name: David

Example: Counting the number of objects of a class

Output:

The number of students: 3

Python Non-Parameterized Constructor Example

Output:

This is non parametrized constructor
Hello John

Python Parameterized Constructor Example

Output:

This is parametrized constructor
Hello John

Python In-built class functions

The in-built functions defined in the class are described in the following table.

SN Function Description
1 getattr(obj,name,default) It is used to access the attribute of the object.
2 setattr(obj, name,value) It is used to set a particular value to the specific attribute of an object.
3 delattr(obj, name) It is used to delete a specific attribute.
4 hasattr(obj, name) It returns true if the object contains some specific attribute.

Example

Output:

John
23
True
AttributeError: 'Student' object has no attribute 'age'

Built-in class attributes

Along with the other attributes, a python class also contains some built-in class attributes which provide information about the class.

The built-in class attributes are given in the below table.

SN Attribute Description
1 __dict__ It provides the dictionary containing the information about the class namespace.
2 __doc__ It contains a string which has the class documentation
3 __name__ It is used to access the class name.
4 __module__ It is used to access the module in which, this class is defined.
5 __bases__ It contains a tuple including all base classes.

Example

Output:

None
{'name': 'John', 'id': 101, 'age': 22}
__main__
Next TopicPython Inheritance




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