我正在开发一个数据库程序,它将对象存储在一个pickle文件中。这些对象有三个属性:名称、等级和平均值。我已经能够将每个学生对象保存到一个pickle文件中,并且我可以读回该文件并显示其内容。但是,我不知道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,则第二个对象将被删除。)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。当我尝试删除一个学生时,我得到了以下错误: TypeError:' student‘对象不支持项目删除。有人知道如何从我的pickle文件中删除对象吗?
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)
发布于 2018-06-04 05:18:18
不能直接从Pickle文件中删除对象。我的意思是,你可以这样做,但它需要你解析它的结构,以确定各个对象的数据开始和结束的位置。这很单调乏味,也不是很有价值。
不过,您可以做的是将所有被腌制的学生作为一个列表读取:
students = list(unpickle_database(filename))
然后,使用del students[index]
从列表中删除一个学生,最后使用该列表重新挑选所有剩余的学生:
for student in students:
save_object(student, filename)
https://stackoverflow.com/questions/50671010
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