Question

我正在研究一个将对象存储在pickle文件中的数据库程序。对象有三个属性：Name，Grade和Average。我已经能够将每个Student对象保存到pickle文件中，然后我可以读回文件并显示它的内容。但是，我无法弄清楚如何使用索引号从文件中删除对象。我希望用户能够键入一个数字，然后删除该编号的对象（因此，如果我键入2，则删除第二个对象。）现在我的代码能够从pickle列表中删除一个项目，但是我不能让它与一个对象一起工作。当我尝试删除学生时，我收到以下错误：TypeError：＆＃39; Student＆＃39;对象不支持删除项目。有谁知道如何从我的pickle文件中删除一个对象？

我的代码如下：

import pickle

class Student():
    def __init__(self,nam,grd,avg):
        self.name = nam
        self.grade = grd
        self.average = avg

    def get_details(self):
        print(self.name, self.grade, self.average)

    def create_item():
        new_student = Student(input("Enter name: "),input("Enter grade: "), input("Enter average: "))
        save_object(new_student, 'student_data.pkl')

    def clear_database():
        file = open('student_data.pkl', 'w')
        file.close()

def save_object(obj, filename):
    with open(filename, 'ab') as output:
        pickle.dump(obj, output, pickle.HIGHEST_PROTOCOL)

def unpickle_database(filename):
    with open(filename, 'rb') as f:
        while True:
            try:
                yield pickle.load(f)
            except EOFError:
                break

def display_database():
    print("\nName:               Grade:              Average:            ")
    for student in unpickle_database('student_data.pkl'):
        property_list = [student.name, student.grade, student.average]
        print(''.join([v.ljust(20,' ') for v in property_list]))

def delete_student(student_to_delete):
    with open('student_data.pkl', 'rb') as f:
        db = pickle.load(f)
    try:
        del db[student_to_delete]
    except KeyError:
        print("{user} doesn't exist in db".format(user=user_to_delete))

while True:
    user_input = input("\nType \"Clear\" to clear the database. Type \"Add\" to add a student. Type \"Display\" to display the database contents. Type \"Quit\" to quit the program. Type \"Remove\" to remove a student.\n")
    if user_input == "Quit":
        break
    if user_input == "Clear":
        Student.clear_database()
        print("\nThe database has been cleared.")
    elif user_input == "Add":
        Student.create_item()
        display_database()
    elif user_input == "Display":
        display_database()
    elif user_input == "Remove":
        student_to_delete = input("Type the student number that you would like to delete: ")
        delete_student(student_to_delete)

Answer 1

您无法直接从Pickle文件中删除对象。我的意思是，您可以这样做，但它需要您解析其结构以确定单个对象的数据开始和结束的位置。这很乏味，也不是很有价值。

但是，您可以做的是将所有被腌制的学生作为列表阅读：

students = list(unpickle_database(filename))

然后，使用del students[index]从列表中删除其中一个学生，最后使用所述列表重新选择所有剩余的学生：

for student in students: save_object(student, filename)

如何使用Python

1 个答案: