How do I write a function to delete a record from a binary file using pickle?

Question

I am storing the records in form of a list.

Write a menu driven program to append, display and delete student details [id, name, percentage] in a binary file. Deletion should be done on the basis of student id.

So I wrote this:

#Code to append display and delete student details
import pickle
def append():
    f = open("student.bin","ab")
    x = int(input("Enter number of students to be appended: "))
    for i in range(x):
        y = eval(input("Enter details in the form [id, name, percentage]: "))
        pickle.dump(y,f)
    f.close()

def display():
    f = open("student.bin","rb")
    while True:
        try:
            x = pickle.load(f)
            print(x)
        except EOFError:
            break
    f.close()

def delete():
    f = open("student.bin","ab+")
    x = input("Enter id to be deleted: ")
    y = pickle.load(f)
    for i in y:
        if str(i[0]) == str(x):

In the end, I was matching the user input to the matching IDs but I don't know how I should go about deleting the list entirely from the binary file.

Answer 1

Here is one way: reads all the student records from file, remove the one we want to delete, then write the whole list back into file.

def delete():
    student_id = int(input("Enter id to be deleted: "))
    records = []
    with open("student.bin", "rb") as stream:
        while True:
            try:
                record = pickle.load(stream)
                if record[0] != student_id:
                    records.append(record)
            except EOFError:
                break
    
    # records now contains all students, except for the one we want to delete
    with open("student.bin", "wb") as stream:
        for record in records:
            pickle.dump(record, stream)

Another way is to open the file for read/write and load each record and write it back. It is harder to understand.