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Asked:2022-08-15 14:56:36 +0000 UTC2022-08-15 14:56:36 +0000 UTC

如何在魔术方法中获取变量

  • 772

有一个学生

class Student:
    def __init__(self, name, surname, gender):
        self.name = name
        self.surname = surname
        self.gender = gender
        self.finished_courses = []
        self.courses_in_progress = []
        self.grades = {}

    def __str__(self):
        average_grade = sum(elem for num in self.grades.values() for elem in num) / len(
            [elem for num in self.grades.values() for elem in num])
        return f'''Имя: {self.name}
Фамилия: {self.surname}
Средняя оценка за домашние задания: {average_grade}
Курсы в процессе изучения: {self.courses_in_progress}
Завершенные курсы: {self.finished_courses}'''

我需要它的 average_grade 变量来按平均成绩比较学生。但如果你把它放进去，它就会__init__开始发誓division by zero。有没有办法把它弄出来__str__？

python ооп

2 个回答

  1. Best Answer

    您可以添加一个方法来计算平均分：

    class Student:
    def __init__(self, name, surname, gender):
        self.name = name
        self.surname = surname
        self.gender = gender
        self.finished_courses = []
        self.courses_in_progress = []
        self.grades = {}

    def get_average_grade(self):
        return sum(elem for num in self.grades.values() for elem in num) / len(
            [elem for num in self.grades.values() for elem in num])

    def __str__(self):
        return f'''Имя: {self.name}
Фамилия: {self.surname}
Средняя оценка за домашние задания: {self.get_average_grade()}
Курсы в процессе изучения: {self.courses_in_progress}
Завершенные курсы: {self.finished_courses}'''

    然后在需要的地方调用它。

    或者制作一个计算字段 - 相同的方法，但使用 decorator @property。将其视为普通字段：

    class Student:
    def __init__(self, name, surname, gender):
        self.name = name
        self.surname = surname
        self.gender = gender
        self.finished_courses = []
        self.courses_in_progress = []
        self.grades = {}

    @property
    def average_grade(self):
        return sum(elem for num in self.grades.values() for elem in num) / len(
            [elem for num in self.grades.values() for elem in num])

    def __str__(self):
        return f'''Имя: {self.name}
Фамилия: {self.surname}
Средняя оценка за домашние задания: {self.average_grade}
Курсы в процессе изучения: {self.courses_in_progress}
Завершенные курсы: {self.finished_courses}'''

    最好将表达式elem for num in self.grades.values() for elem in num放入一个单独的变量中，计算一次，然后将其和除以它的长度：

        @property
    def average_grade(self):
        grades = [elem for num in self.grades.values() for elem in num]
        return sum(grades) / len(grades)
    • 2

  2. 作为一个选项，初始化一个私有变量，该变量将被赋值并通过特殊方法返回

    例子：

    class Student:
    def __init__(self, name, surname, gender):
        self.name = name
        self.surname = surname
        self.gender = gender
        self.finished_courses = []
        self.courses_in_progress = []
        self.grades = {}
        self.__average_grade = None

    def aver(self):
        return self.__average_grade
    def __str__(self):
        average_grade = sum(elem for num in self.grades.values() for elem in num) / len(
            [elem for num in self.grades.values() for elem in num])
        self._average_grade = average_grade
        return f'''Имя: {self.name}
Фамилия: {self.surname}
Средняя оценка за домашние задания: {average_grade}
Курсы в процессе изучения: {self.courses_in_progress}
Завершенные курсы: {self.finished_courses}'''

st = Student('Евгений', 'Малевичев', 'Male')
print(st.aver())
    • 0

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