|
一、字典、元组的多重嵌套
例 1:记录全班学生的成绩。
分析:定义一个 SimpleGradebook类,
学生名是字典self._grades的键,成绩是字典self._grades的值。- class SimpleGradebook():
- def __init__(self):
- self._grades = {}
- def add_student(self, name):
- self._grades[name] = []
- def report_grade(self, name, score):
- self._grades[name].append(score)
- def average_grade(self, name):
- grades = self._grades[name]
- return self._grades, sum(grades) / len(grades)
复制代码- book = SimpleGradebook()
- book.add_student('qinlu')
- book.report_grade('qinlu', 99)
- print(book.average_grade('qinlu'))
复制代码 字典可能因为功能过多导致结果多重嵌套。
例 2:扩充 SimpleGradebook类,按科目保存成绩。
分析:定义一个 BySubjectGradebook类,字典by_subject嵌套在字典self._grades内。
学生名是字典self._grades的键,科目、成绩是self._grades的值。
科目是字典by_subject的键,成绩是字典by_subject的值。- class BySubjectGradebook():
- """
- report_grade(), average_grade()嵌套了两层的字典
- """
- def __init__(self):
- self._grades = {}
- def add_student(self, name):
- self._grades[name] = {}
- def report_grade(self, name, subject, score):
- by_subject = self._grades[name]
- grade_list = by_subject.setdefault(subject, [])
- grade_list.append(score)
- def average_grade(self, name):
- by_subject = self._grades[name]
- total, count = 0, 0
- for scores in by_subject.values():
- total += sum(scores)
- count += len(scores)
- return self._grades, total / count
复制代码- book = BySubjectGradebook()
- book.add_student('qinlu')
- book.report_grade('qinlu', 'Math', 99)
- book.report_grade('qinlu', 'Math', 88)
- book.report_grade('qinlu', 'Computer', 90)
- book.report_grade('qinlu', 'Computer', 80)
- print(book.average_grade('qinlu'))
复制代码- ({'qinlu': {'Math': [99, 88], 'Computer': [90, 80]}}, 89.25)
复制代码 例 3:需求变更,需记录每次成绩占总成绩的权重。(期中、期末考试所占的分量比随堂考大)
- class WeightedGradebook():
- def __init__(self):
- self._grades = {}
- def add_student(self, name):
- self._grades[name] = {}
- def report_grade(self, name, subject, score, weight):
- by_subject = self._grades[name]
- grade_list = by_subject.setdefault(subject, [])
- grade_list.append(score, weight)
- def average_grade(self, name):
- by_subject = self._grades[name]
- score_sum, score_count = 0, 0
- for subject, scores in by_subject.items():
- subject_avg, total_weight = 0, 0
- for score, weight in scores:
- #...
- return score_sum / score_count
复制代码- book = WeightedGradebook()
- book.add_student('qinlu')
- book.report_grade('qinlu', 'Math', 99, 0.1)
- book.report_grade('qinlu', 'Math', 88, 0.6)
- book.report_grade('qinlu', 'Computer', 90, 0.1)
- book.report_grade('qinlu', 'Computer', 80, 0.6)
- print(book.average_grade('qinlu'))
复制代码 该代码出现字典、元组的多层嵌套,应拆解为类。多层嵌套的代码,很难维护。
二、嵌套结构重构为类
将下面的字典重构为类。
字典by_subject嵌套在字典self._students内。- {'qinlu': {'Math': [(99, 0.1), (88, 0.9)], 'Computer': [(90. 0.1), (80, 0.9)]}}
复制代码 分析:
- Gradebook()类,学生名是字典self._students的键;科目、成绩、权重是self._grades的值。
- Student()类,科目是字典self._subjects的键;成绩、权重是self._subjects的值。
- Subject()类,成绩是列表self._grades的第一位;权重是列表self._grades的第二位。
从最底层开始重构,即考试成绩。这么简单的信息,没必要写成类。
namedtuple()命名元组。- from collections import namedtuple
- #学习中遇到问题没人解答?小编创建了一个Python学习交流群:153708845
- Grade = namedtuple('Grade', ('score', 'weight'))
- # 科目类,该类包含考试成绩
- class Subject():
- 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
- # print(self._grades)
- for grade in self._grades:
- # print(grade)
- total += grade.score * grade.weight
- total_weight += grade.weight
- return total / total_weight
- # 学生类,该类包含学习课程
- class Student():
- 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
- # 成绩册类,包含所有学生考试成绩的容器类,该容器类以学生名字为键,可动态添加学生
- class Gradebook():
- 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()
- qin = book.student('qinlu')
- math = qin.subject('Math')
- math.report_grade(99, 0.1)
- math.report_grade(88, 0.9)
- print(qin.average_grade())
复制代码 虽然代码量是原来的两倍,但更清晰,更易扩展,理解起来比原来容易。
来源:https://www.cnblogs.com/python1111/p/18191668
免责声明:由于采集信息均来自互联网,如果侵犯了您的权益,请联系我们【E-Mail:cb@itdo.tech】 我们会及时删除侵权内容,谢谢合作! |
|