Builder Design Pattern implemented using Python...

Today I am presenting the Builder Pattern in Python.

As the name suggests - it is part of the creational pattern.

The idea is that if a class has many member variables - and the final object may not depend on all of them - and the number of parameters that the constructor takes varies - instead of making a lot of overloaded constructors, we use this Builder pattern

The code footprint is heavily reduced - as there is no need to create a matching number of overloaded constructors to match each and every permutation and combination of the member variables passed in the constructors.

In the given example, we have created a common Student class which may represent a 10th std, a 12th std, or an engineering student - maybe in 1st yr or 2nd year, or third year or maybe in the final fourth year.

In the case of a student who is a qualified engineer, we need to supply all the marks…

But in the case of a 2nd-year student - we don’t need to bother about third-year marks or fourth-year marks, the 10th, 12th, and 1st-year marks are sufficient to represent the object of a second-year student vis-a-vis marks.

Here goes the code for the CS students of the UNIVERSE.

from abc import ABC, abstractmethod

class Student:
    class Builder:
        def __init__(self):
            self.name = ""
            self.address = ""
            self.tenthmarks = 0
            self.twelfthmarks = 0
            self.firstyrmarks = 0
            self.secondyrmarks = 0
            self.thirdyrmarks = 0
            self.fourthyrmarks = 0

        def setname(self, name):
            self.name = name
            return self

        def setaddress(self, address):
            self.address = address
            return self

        def settenthmarks(self, tenthmarks):
            self.tenthmarks = tenthmarks
            return self

        def settwelfthmarks(self, twelfthmarks):
            self.twelfthmarks = twelfthmarks
            return self

        def setfirstyrmarks(self, firstyrmarks):
            self.firstyrmarks = firstyrmarks
            return self

        def setsecondyrmarks(self, secondyrmarks):
            self.secondyrmarks = secondyrmarks
            return self

        def setthirdyrmarks(self, thirdyrmarks):
            self.thirdyrmarks = thirdyrmarks
            return self

        def setfourthyrmarks(self, fourthyrmarks):
            self.fourthyrmarks = fourthyrmarks
            return self

        def build(self):
            return Student(self)

    def __init__(self, builder):
        self.name = builder.name
        self.address = builder.address
        self.tenthmarks = builder.tenthmarks
        self.twelfthmarks = builder.twelfthmarks
        self.firstyrmarks = builder.firstyrmarks
        self.secondyrmarks = builder.secondyrmarks
        self.thirdyrmarks = builder.thirdyrmarks
        self.fourthyrmarks = builder.fourthyrmarks

    def displayData(self):
        if self.name != "":
            print("Name :", self.name)
        if self.address != "":
            print("Address :", self.address)
        if self.tenthmarks != 0:
            print("10th Marks :", self.tenthmarks)
        if self.twelfthmarks != 0:
            print("12th Marks :", self.twelfthmarks)
        if self.firstyrmarks != 0:
            print("1st Yr Marks :", self.firstyrmarks)
        if self.secondyrmarks != 0:
            print("2nd Yr Marks :", self.secondyrmarks)
        if self.thirdyrmarks != 0:
            print("3rd Yr Marks :", self.thirdyrmarks)
        if self.fourthyrmarks != 0:
            print("4th Yr Marks :", self.fourthyrmarks)

# Press the green button in the gutter to run the script.
if __name__ == '__main__':
    ram12th = Student.Builder().setname("Ram").setaddress("Kolkata").settenthmarks(50).build()
    shyam2ndYr = Student.Builder().setname("Shyam").setaddress("Delhi").settenthmarks(70).settwelfthmarks(78).setfirstyrmarks(70).build()

    ram12th.displayData()
    shyam2ndYr.displayData()

If we run the above program, the output will be as follows:

Name : Ram

Address : Kolkata

10th Marks : 50

Name : Shyam

Address : Delhi

10th Marks : 70

12th Marks : 78

1st Yr Marks : 70

As it is clear for Ram, till 10th marks was important whereas, for Shyam, on the other hand, marks till 1st year are important.