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March 25, 2020 12:45
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Composing classes with dataclass, instead of deep-nested dictionary
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| # From the book, effective python 2nd edition item 37 | |
| from collections import defaultdict | |
| from dataclasses import dataclass, field | |
| from typing import List, Dict | |
| @dataclass | |
| class Grade: | |
| weight: int | |
| score: int | |
| @dataclass | |
| class Subject: | |
| grades: List[Grade] = field(default_factory=list) | |
| def report_grade(self, weight, score): | |
| grade = Grade(weight=weight, score=score) | |
| self.grades.append(grade) | |
| def average_grade(self): | |
| total_weight, total_count = 0, 0 | |
| for grade in self.grades: | |
| total_count += grade.weight * grade.score | |
| total_weight += grade.weight | |
| return total_count / total_weight | |
| @dataclass | |
| class Student: | |
| subjects: Dict[str, Subject] = field(default_factory=lambda: defaultdict(Subject)) | |
| def add_subject(self, subject): | |
| normalized_subject = subject.lower() | |
| return self.subjects[normalized_subject] | |
| def average_grade(self): | |
| total, count = 0, 0 | |
| for subject in self.subjects.values(): | |
| total += subject.average_grade() | |
| count += 1 | |
| return total / count | |
| @dataclass | |
| class GradeBook: | |
| students: Dict[str, Student] = field(default_factory=lambda: defaultdict(Student)) | |
| def add_student(self, name): | |
| normalized_name = name.lower() | |
| return self.students[normalized_name] | |
| book = GradeBook() | |
| albert = book.add_student('Albert Einstein') | |
| math = albert.add_subject('Math') | |
| math.report_grade(weight=0.05, score=75) | |
| math.report_grade(weight=0.15, score=65) | |
| math.report_grade(weight=0.80, score=70) | |
| gym = albert.add_subject('Gym') | |
| gym.report_grade(weight=0.40, score=100) | |
| gym.report_grade(weight=0.60, score=85) | |
| assert albert.average_grade() == 80.25 |
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this is nice example. I searched all over internet to find such an example.
This is almost of the same structure i am building.