freeCodeCamp/guide/english/software-engineering/design-patterns/builder/index.md

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Builder

The builder is a design pattern that could abstract and decouple the creation of a very complex object.

Builder in Python

Here is an example of Builder Pattern implementation in Python3.

# Builder
class CourseBuilder(object):
    def __init__(self, teacher):
        self.teacher = teacher

    def build_course(self):
        self.teacher.provide_homework()
        self.teacher.provide_exam()
        return self.teacher.course

# Teacher
class Teacher(object):
    def __init__(self, name=None):
        self.name = name
        self.course = Course()

    def provide_homework(self):
        raise NotImplementedError

    def provide_exam(self):
        raise NotImplementedError


class MathTeacher(Teacher):
    def provide_homework(self):
        self.course.homework = 'This is Math homework provided by {}.'.format(self.name)

    def provide_exam(self):
        self.course.exam = 'This is Math exam tested by {}.'.format(self.name)


class HistoryTeacher(Teacher):
    def provide_homework(self):
        self.course.homework = 'This is History homework provided by {}.'.format(self.name)

    def provide_exam(self):
        self.course.exam = 'This is History exam tested by {}.'.format(self.name)


# Target objects to be produced
class Course(object):
    def __init__(self):
        self.homework = None
        self.exam = None

    def __str__(self):
        return 'Homework: {}\nExam: {}\n'.format(self.homework, self.exam)


math_course = CourseBuilder(MathTeacher('Harry')).build_course()
print(math_course)
>>> Homework: This is Math homework provided by Harry.
>>> Exam: This is Math exam tested by Harry.

history_course = CourseBuilder(HistoryTeacher('Potter')).build_course()
print(history_course)
>>> Homework: This is History homework provided by Potter.
>>> Exam: This is History exam tested by Potter.