Item 22: Prefer Helper Classes Over Bookkeeping with Dictionaries and Tuples from Effective Python written by Brett Slatkin

gradebook.py

# This code is from
# Item 22: Prefer Helper Classes Over Bookkeeping with
#          Dictionaries and Tuples
# from Effective Python written by Brett Slatkin
# 2015

import collections


Grade = collections.namedtuple('Grade', ('score', 'weight'))


class Subject(object):
    def __init__(self):
        self._grades = []
        
    def report_grade(self, score, weight):
        self._grades.append(Grade(score, weight))
        
    def average_grade(self):
        total, total_weight = 0, 0
        for grade in self._grades:
            total += grade.score * grade.weight
            total_weight += grade.weight
        return total / total_weight
    

class Subject(object):
    def __init__(self):
        self._grades = []
        
    def report_grade(self, score, weight):
        self._grades.append(Grade(score, weight))
        
    def average_grade(self):
        total, total_weight = 0, 0
        for grade in self._grades:
            total += grade.score * grade.weight
            total_weight += grade.weight
        return total / total_weight
    

class Student(object):
    def __init__(self):
        self._subjects = {}
        
    def subject(self, name):
        if name not in self._subjects:
            self._subjects[name] = Subject()
        return self._subjects[name]
    
    def average_grade(self):
        total, count = 0, 0
        for subject in self._subjects.values():
            total += subject.average_grade()
            count += 1
        return total / count
    
    
class Gradebook(object):
    def __init__(self):
        self._students = {}
        
    def student(self, name):
        if name not in self._students:
            self._students[name] = Student()
        return self._students[name]
    
    
book = Gradebook()
albert = book.student('Albert Einstein')
math = albert.subject('Math')
math.report_grade(80, 0.10)
print(albert.average_grade())