import pickle


# Creating the Record


class CarRecord:

    def __init__(self):
        self.VehicleID=""
        self.Registration=""
        self.DateOfRegistration = None
        self.EngineSize = 0
        self.PurchasePrice = 0.00

CarsArray=["" for i in range(2)]   #Creating the array

#Creating the binary file
CarsFile=open("CarsRAND.dat", 'wb')


#Assigning each array element to the class

for i in range(2):
    CarsArray[i]= CarRecord()
    VehicleID=str(input("Enter Vehicle ID"))
    CarsArray[i].VehicleID=(VehicleID)
    print ("Vehicle ID:", i, CarsArray[i].VehicleID, " has been entered")

#writing each record to the file
for i in range(2):
    Address=hash(CarsArray[i].VehicleID) #Hashing address
    print("Address: ", str(i), Address)
    CarsFile.seek(Address) #Seeking hashed address
    pickle.dump(CarsArray[i],CarsFile) #Putting record in hashed address


CarsFile.close


# Reading record from hashed address.
CarsFile=open("CarsRND.dat", 'rb')
VehicleID=str(input("Enter Vehicle ID to Load"))
Address=hash(VehicleID)
CarsFile.seek(Address)
Record = pickle.load(CarsFile)
print(Record.VehicleID)

CarsFile.close
        

(Nov-03-2021, 04:58 PM)Gribouillis Wrote: I don't understand the call to seek() in the file with an offset equal to the hash() of some data called VehicleID. What is the purpose of this call? It will obviously lead to invalid operations on the file.

Python_help Wrote:The seek part creates the address in the file

(Nov-03-2021, 05:18 PM)Gribouillis Wrote:

Python_help Wrote:The seek part creates the address in the file

We don't have the same notion of files' seek() function. As far as I know it can only set the file's position to an existing position in the file, not create a position, or an address.

with open("test.bin", "wb") as file:
    file.seek(32)
    file.write(b"Where's Waldo")

Output:
Dump
................
................
Where's Waldo

x = "one"
y = "two"
print(hash(x), hash(y), id(x), id(y))

Output:
6029220552427752314 -4114662839508124676 1827875350256 1827875262064