A Class is a logical grouping of data and functions. It gives the freedom to create data structures that contains arbitrary content and hence easily accessible.
For example, for any bank employee who want to fetch the customer details online would go to customer class, where all its attributes like transaction details, withdrawal and deposit details, outstanding debt, etc. would be listed out.
In this tutorial, we will learn,
To define class you need to consider following points
Step 1) In Python, classes are defined by the "Class" keyword
class myClass():
Step 2) Inside classes, you can define functions or methods that are part of this class
def method1 (self): print "Guru99" def method2 (self,someString): print "Software Testing:" + someString
Step 3) Everything in a class is indented, just like the code in the function, loop, if statement, etc. Anything not indented is not in the class
NOTE: About using "self" in Python
Step 4) To make an object of the class
c = myClass()
Step 5) To call a method in a class
c.method1() c.method2(" Testing is fun")
Step 6) Here is the complete code
# Example file for working with classes class myClass(): def method1(self): print("Guru99") def method2(self,someString): print("Software Testing:" + someString) def main(): # exercise the class methods c = myClass () c.method1() c.method2(" Testing is fun") if __name__== "__main__": main()
Inheritance is a feature used in object-oriented programming; it refers to defining a new class with less or no modification to an existing class. The new class is called derived class and from one which it inherits is called the base. Python supports inheritance; it also supports multiple inheritances. A class can inherit attributes and behavior methods from another class called subclass or heir class.
Python Inheritance Syntax
class DerivedClass(BaseClass): body_of_derived_class
Step 1) Run the following code
# Example file for working with classes class myClass(): def method1(self): print("Guru99") class childClass(myClass): #def method1(self): #myClass.method1(self); #print ("childClass Method1") def method2(self): print("childClass method2") def main(): # exercise the class methods c2 = childClass() c2.method1() #c2.method2() if __name__== "__main__": main()
Notice that the in childClass, method1 is not defined but it is derived from the parent myClass. The output is "Guru99."
Step 2) Uncomment Line # 8 & 10. Run the code
Now, the method 1 is defined in the childClass and output "childClass Method1" is correctly shown.
Step 3) Uncomment Line #9. Run the code
You can a method of the parent class using the syntax
ParentClassName.MethodName(self)
In our case, we call, myClass.method1(self) and Guru99 is printed as expected
Step 4) Uncomment Line #19. Run the code.
Method 2 of the child class is called and "childClass method2" is printed as expected.
A constructor is a class function that instantiates an object to predefined values.
It begins with a double underscore (_). It __init__() method
In below example we are taking name of the user using constructor.
class User: name = "" def __init__(self, name): self.name = name def sayHello(self): print("Welcome to Guru99, " + self.name) User1 = User("Alex") User1.sayHello()
Output will be:
Welcome to Guru99, Alex
Python 2 Example
Above codes are Python 3 examples, If you want to run in Python 2 please consider following code.
# How to define Python classes # Example file for working with classes class myClass(): def method1(self): print "Guru99" def method2(self,someString): print "Software Testing:" + someString def main(): # exercise the class methods c = myClass () c.method1() c.method2(" Testing is fun") if __name__== "__main__": main() #How Inheritance works # Example file for working with classes class myClass(): def method1(self): print "Guru99" class childClass(myClass): #def method1(self): #myClass.method1(self); #print "childClass Method1" def method2(self): print "childClass method2" def main(): # exercise the class methods c2 = childClass() c2.method1() #c2.method2() if __name__== "__main__": main()
"Class" is a logical grouping of functions and data. Python class provides all the standard features of Object Oriented Programming.