In this chapter, we are going to use Object Oriented Programming(OOP) features of Python. You will become an expert in Python OOP.<\/p>\n
So we’ll cover the following<\/p>\n
<\/p>\n
Let’s reviews some of the important OOP terms.<\/p>\n
Class<\/strong> – A blueprint for creating new object. A class defines the attributes and behaviors of an object. The attributes are data members (instance and class variables). The behavior is represented by methods(or member functions)<\/p>\n Class Variable<\/strong> – This is a variable that is shared by all objects created from the class. You define class variables inside the class but outside any of the methods.<\/p>\n Data Member<\/strong> – This are variables defined in the class. They are used to hold data associated with the specific class<\/p>\n Function Overloading<\/strong> – You use function overloading to create two functions with same name. But they perform different operations based on its arguments<\/p>\n Instance Variable<\/strong> – These is a variable that is defined in a class but belongs only to the particular instance of the class.<\/p>\n Instance<\/strong> – An object created from a class<\/p>\n Inheritance<\/strong> – The feature that allows a class to inherit the properties of another class. The parent class is called the super class while the child class is called sub class.<\/p>\n Instantiation<\/strong> – The process of creating an instance (object of a class)<\/p>\n Operator Overloading<\/strong> – The process where an operator performs more than one type of operation<\/p>\n <\/p>\n You create a class using the class statement<\/p>\n Listing 1.0: Definition of the Student Class<\/p>\n <\/p>\n Let’s understand some parts of this class definition<\/p>\n noOfStudents:\u00a0 this is a class variable. Therefore it belongs to the class. It’s value is shared by all objects created from this class. You can access it using the class name. For example, Student.noOfStudents<\/em>. Also, just one copy\u00a0 exist in memory.<\/p>\n __init__ (): This is a special function. It is called a constructor. It is called when the class is instantiated.<\/p>\n self: this refers to the current class<\/p>\n <\/p>\n Now that we have our class defined, we can then create objects from the class. To do this, you call the class using its name. Then you pass the arguments as defined in the __init__ function.<\/p>\n For example, we create and display two student objects<\/p>\n <\/p>\n <\/p>\n Listing 1.1: Creating objects and accessing attributes<\/p>\n <\/p>\n <\/p>\n You can notice that in the Listing 1.1 above, we create two objects, student1 and student2. Then we access the attributes printStudent() and noOfStuents.<\/p>\n But you can also use certain functions defined in Python to access attributes. These functions are given in the table below.<\/p>\n <\/p>\n <\/p>\n <\/p>\n Python provides some built-in attributes that you can use for certain operation. Just like normal attributes, these built-in attributes can be accessed the same way.<\/p>\n We now used these in-built attributes for the Student class\u2212<\/p>\n <\/p>\n Listing 1.2: Using inbuilt attributes<\/p>\n <\/p>\n If you run the code in Listing 1.2, you will have the following output<\/p>\n <\/p>\n2. Creating a Class<\/strong><\/h4>\n
'Creating an new Class'<\/span>\r\nclass<\/span> Student<\/span>:\r\n 'Common base class for all students'<\/span>\r\n noOfStudents =<\/span> 0<\/span>\r\n\r\n def<\/span> __init__<\/span>(self<\/span>, regno, firstname, lastname):\r\n self<\/span>.<\/span>regno =<\/span> regno\r\n self<\/span>.<\/span>firstname =<\/span> firstname\r\n self<\/span>.<\/span>lastname =<\/span> lastname\r\n Student.<\/span>noOfStudents +=<\/span> 1<\/span>\r\n\r\n def<\/span> displayCount<\/span>(self<\/span>):\r\n print<\/span>(\"Total Students %d\"<\/span> %<\/span> Student.<\/span>noOfStudents)\r\n\r\n def<\/span> printStudent<\/span>(self<\/span>):\r\n print<\/span>(\"Reg. Number: \"<\/span> +<\/span> self<\/span>.<\/span>regno, \"Name: \"<\/span> +<\/span> self<\/span>.<\/span>firstname +<\/span> \" \"<\/span> +<\/span> self<\/span>.<\/span>lastname)\r\n<\/pre>\n3. Creating Objects from a Class (Instantiation)<\/strong><\/h4>\n
student1 =<\/span> Student(\"001\"<\/span>, \"Solace\"<\/span>, \"Okeke\"<\/span>)\r\nstudent2 =<\/span> Student(\"002\"<\/span>, \"Treasure\"<\/span>, \"Munonye\"<\/span>)\r\n\r\nstudent1.<\/span>printStudent()\r\nstudent2.<\/span>printStudent()\r\n\r\nprint<\/span>(\"Number of Students: %d\"<\/span> %<\/span>(Student.<\/span>noOfStudents))\r\n<\/pre>\n4. Accessing Attributes<\/strong><\/h4>\n
\n\n
\n getattr(object, name):<\/strong> used to access the attribute of the object<\/td>\n<\/tr>\n \n hasattr(object, name):<\/strong> used to check if an attribute exists<\/td>\n<\/tr>\n \n setattr(object, name, value):<\/strong> assigns an attribute. If the attribute does not exits, then\u00a0 it is created<\/td>\n<\/tr>\n \n delattr(object, name):<\/strong> deletes an attribute<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n hasattr<\/span>(student1, 'grade'<\/span>) # returns False<\/span>\r\ngetattr<\/span>(student1, 'firstname'<\/span>) # returns Solace<\/span>\r\n\r\nsetattr<\/span>(student1, 'firstname'<\/span>, 'Oleander'<\/span>) # changes the lastname to Oleander<\/span>\r\n\r\ndelattr<\/span>(student1, 'lastname'<\/span>) # deletes the lastname attribute<\/span>\r\n<\/pre>\n5. Built-in Class Attribute<\/strong><\/h4>\n
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'Creating an new Class'<\/span>\r\nclass<\/span> Student<\/span>:\r\n 'Common base class for all students'<\/span>\r\n noOfStudents =<\/span> 0<\/span>\r\n\r\n def<\/span> __init__<\/span>(self<\/span>, regno, firstname, lastname):\r\n self<\/span>.<\/span>regno =<\/span> regno\r\n self<\/span>.<\/span>firstname =<\/span> firstname\r\n self<\/span>.<\/span>lastname =<\/span> lastname\r\n Student.<\/span>noOfStudents +=<\/span> 1<\/span>\r\n\r\n def<\/span> displayCount<\/span>(self<\/span>):\r\n print<\/span>(\"Total Students %d\"<\/span> %<\/span> Student.<\/span>noOfStudents)\r\n\r\n def<\/span> printStudent<\/span>(self<\/span>):\r\n print<\/span>(\"Reg. Number: \"<\/span> +<\/span> self<\/span>.<\/span>regno, \"Name: \"<\/span> +<\/span> self<\/span>.<\/span>firstname +<\/span> \" \"<\/span> +<\/span> self<\/span>.<\/span>lastname)\r\n\r\n\r\nprint<\/span>(\"Student.__doc__:\"<\/span>, Student.<\/span>__doc__)\r\nprint<\/span>(\"Student.__name__:\"<\/span>, Student.<\/span>__name__)\r\nprint<\/span>(\"Student.__module__:\"<\/span>, Student.<\/span>__module__)\r\nprint<\/span>(\"Student.__bases__:\"<\/span>, Student.<\/span>__bases__)\r\nprint<\/span>(\"Student.__dict__:\"<\/span>, Student.<\/span>__dict__)\r\n<\/pre>\nStudent.<\/span>__doc__: Common base class<\/span> for<\/span> all<\/span> students\r\nStudent.<\/span>__name__: Student\r\nStudent.<\/span>__module__: __main__\r\nStudent.<\/span>__bases__: (<<\/span>class<\/span> '<\/span>object<\/span>'>,)<\/span>\r\nStudent.<\/span>__dict__: {'__module__'<\/span>: '__main__'<\/span>, '__doc__'<\/span>: 'Common base class for all students'<\/span>, 'noOfStudents'<\/span>: 0<\/span>, '__init__'<\/span>: <<\/span>function Student.<\/span>__init__ at 0x000001B37FF81E18<\/span>><\/span>, 'displayCount'<\/span>: <<\/span>function Student.<\/span>displayCount at 0x000001B37FF81F28<\/span>><\/span>, 'printStudent'<\/span>: <<\/span>function Student.<\/span>printStudent at 0x000001B37FF892F0<\/span>><\/span>, '__dict__'<\/span>: <<\/span>attribute '__dict__'<\/span> of 'Student'<\/span> objects><\/span>, '__weakref__'<\/span>: <<\/span>attribute '__weakref__'<\/span> of