int which translates to saying that variables that store integers are variables which are instances (objects) of the int class.Note for Static Language ProgrammersNote that even integers are treated as objects (of theintclass). This is unlike C++ and Java (before version 1.5) where integers are primitive native types.Seehelp(int)for more details on the class.C# and Java 1.5 programmers will find this similar to the boxing and unboxing concept.
class keyword. The fields and methods of the class are listed in an indented block.selfself.self - any other name is definitely frowned upon. There are many advantages to using a standard name - any reader of your program will immediately recognize it and even specialized IDEs (Integrated Development Environments) can help you if you use self.Note for C++/Java/C# ProgrammersTheselfin Python is equivalent to thethispointer in C++ and thethisreference in Java and C#.
self and why you don't need to give a value for it. An example will make this clear. Say you have a class called MyClass and an instance of this class called myobject. When you call a method of this object as myobject.method(arg1, arg2), this is automatically converted by Python into MyClass.method(myobject, arg1, arg2) - this is all the special self is about.self.oop_simplestclass.py).class statement and the name of the class. This is followed by an indented block of statements which form the body of the class. In this case, we have an empty block which is indicated using the pass statement.Person class in the __main__ module.self variable. We will now see an example (save as oop_method.py).self in action. Notice that the say_hi method takes no parameters but still has the self in the function definition.__init__ method__init__ method now.__init__ method is run as soon as an object of a class is instantiated (i.e. created). The method is useful to do any initialization (i.e. passing initial values to your object) you want to do with your object. Notice the double underscores both at the beginning and at the end of the name.oop_init.py):__init__ method as taking a parameter name (along with the usual self). Here, we just create a new field also called name. Notice these are two different variables even though they are both called 'name'. There is no problem because the dotted notation self.name means that there is something called "name" that is part of the object called "self" and the other name is a local variable. Since we explicitly indicate which name we are referring to, there is no confusion.p, of the class Person, we do so by using the class name, followed by the arguments in the parentheses: p = Person('Swaroop').__init__ method. This is the special significance of this method.self.name field in our methods which is demonstrated in the say_hi method.oop_objvar.py):population belongs to the Robot class and hence is a class variable. The name variable belongs to the object (it is assigned using self) and hence is an object variable.population class variable as Robot.population and not as self.population. We refer to the object variable name using self.name notation in the methods of that object. Remember this simple difference between class and object variables. Also note that an object variable with the same name as a class variable will hide the class variable!Robot.population, we could have also used self.__class__.population because every object refers to its class via the self.__class__ attribute.how_many is actually a method that belongs to the class and not to the object. This means we can define it as either a classmethod or a staticmethod depending on whether we need to know which class we are part of. Since we refer to a class variable, let's use classmethod.@classmethod decorator is the same as calling:__init__ method is used to initialize the Robot instance with a name. In this method, we increase the population count by 1 since we have one more robot being added. Also observe that the values of self.name is specific to each object which indicates the nature of object variables.self only. This is called an attribute reference.Robot.__doc__ and the method docstring as Robot.say_hi.__doc__die method, we simply decrease the Robot.population count by 1.__privatevar, Python uses name-mangling to effectively make it a private variable.Note for C++/Java/C# ProgrammersAll class members (including the data members) are public and all the methods are virtual in Python.
SchoolMember and then have the teacher and student classes inherit from this class, i.e. they will become sub-types of this type (class) and then we can add specific characteristics to these sub-types.SchoolMember, this is automatically reflected in the subtypes as well. For example, you can add a new ID card field for both teachers and students by simply adding it to the SchoolMember class. However, changes in the subtypes do not affect other subtypes. Another advantage is that you can refer to a teacher or student object as a SchoolMember object which could be useful in some situations such as counting of the number of school members. This is called polymorphism where a sub-type can be substituted in any situation where a parent type is expected, i.e. the object can be treated as an instance of the parent class.SchoolMember class in this situation is known as the base class or the superclass. The Teacher and Student classes are called the derived classes or subclasses.oop_subclass.py):class Teacher(SchoolMember)). Next, we observe that the __init__ method of the base class is explicitly called using the self variable so that we can initialize the base class part of an instance in the subclass. This is very important to remember- Since we are defining a __init__ method in Teacher and Student subclasses, Python does not automatically call the constructor of the base class SchoolMember, you have to explicitly call it yourself.__init__ method in a subclass, Python will call the constructor of the base class automatically.Teacher or Student as we would an instance of SchoolMember and access the tell method of SchoolMember by simply typing Teacher.tell or Student.tell, we instead define another tell method in each subclass (using the tell method of SchoolMember for part of it) to tailor it for that subclass. Because we have done this, when we write Teacher.tell Python uses the tell method for that subclass vs the superclass. However, if we did not have a tell method in the subclass, Python would use the tell method in the superclass. Python always starts looking for methods in the actual subclass type first, and if it doesnt find anything, it starts looking at the methods in the subclasss base classes, one by one in the order they are specified in the tuple (here we only have 1 base class, but you can have multiple base classes) in the class definition.end parameter is used in the print function in the superclass's tell() method to print a line and allow the next print to continue on the same line. This is a trick to make print not print a \n (newline) symbol at the end of the printing.