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This article will introduce you to an interesting topic that is simple yet core for programming, I am referring to Python constructors. Following pointers will be covered in this article,
If you have been programming for sometime now, you have probably come across the name Python one too many times. Python as a programming language follows object orientation, meaning which every instance that is created on the platform is defined as an object. Although most of the components in Python have a ton of information online, one topic that keep getting researched over and over again is that of a constructor in Python. Therefore in this article we will discuss all about constructors in Python, how you can make use of them and the benefits they bring to the table. Let’s begin!
A constructor can simply be defined as a special type of method or function which can be used to initialize instances of various members in a class.
In Python, there are two different types of constructors.
A constructor is defined the moment we create an object inside a class. The presence of a constructor also verifies that enough resources are present, so that a start up task can easily be executed via an object of a class.
Now that you have acquainted yourself with the definition and types of constructors in Python, let us explore how we can create a constructor in Python.
In Python, if you need to create a construct you need to make use of the __init__ function and or method. You need to call upon this method, the moment a class is instantiated. Once the __init__ function has been defined and called upon, we can pass any number of arguments at the time of creating the class objects depending upon your needs. The most common use of a constructor in Python is to initialize the attributes of a class.
Every class you create in Python needs to have a constructor present in order for it to function, even if it is the default constructor.
To understand this concept better, take a look at the example below.
class Employee: def __init__(self,name,id): self.id = id; self.name = name; def display (self): print("ID: %d nName: %s"%(self.id,self.name)) emp1 = Employee("John",101) emp2 = Employee("David",102) #accessing display() method to print employee 1 information emp1.display(); #accessing display() method to print employee 2 information emp2.display();
When you run the above program, the output will look something like this.
As mentioned in the definitions above, a parameterized constructor is one which has a predefined value and a non parameterized constructor is one which has no value assigned to it. While programming the use cases vary depending upon the context, and to understand this better, take a look at the examples below.
class Student: #Constructor - non parameterized def __init__(self): print("This is non parametrized constructor") def show(self,name): print("Hello",name) student = Student() student.show("John")
The above is an example of a Non-Parameterized Constructor and its output will be the following.
This is non parametrized constructor
class Student: #Constructor - parameterized def __init__(self, name): print("This is parametrized constructor") self.name = name def show(self): print("Hello",self.name) student = Student("John") student.show()
The above is an example of a Parameterized Constructor and its output will be the following.
This is parametrized constructor
Now that the basics of a constructor in Python is clear, let us explore the various inbuilt classes that are present in Python.
To understand the concept of inbuilt class functions in Python, take a look at the code below.
class Student: def __init__(self,name,id,age): self.name = name; self.id = id; self.age = age #creates the object of the class Student s = Student("John",101,22) #prints the attribute name of the object s print(getattr(s,'name')) # reset the value of attribute age to 23 setattr(s,"age",23) # prints the modified value of age print(getattr(s,'age')) # prints true if the student contains the attribute with name id print(hasattr(s,'id')) # deletes the attribute age delattr(s,'age') # this will give an error since the attribute age has been deleted print(s.age)
The output for the above will be.
AttributeError: ‘Student’ object has no attribute ‘age’
Along with the inbuilt class functions, Python comes with inbuilt class attributes, which come in handy at times. Some of the most significant builtin class attributes are as given below.
An example to clarify all the built in class attributes is as given below.
class Student: def __init__(self,name,id,age): self.name = name; self.id = id; self.age = age def display_details(self): print("Name:%s, ID:%d, age:%d"%(self.name,self.id)) s = Student("John",101,22) print(s.__doc__) print(s.__dict__) print(s.__module__)
This brings us to the end of this article on Python Constructors.
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