How can I save all information of a python class to binary?

Question

I'm creating a little shell app to help me save some info and review some python.

I have a couple of python code for a bunch of classes that refer to each other, such as User, Person, Contact, Event and then a main App.py that I use to test it.

I'm using pickle to save the data, using this question as inspiration.

My problem is although the class is saved, it's "internal information isn't".

import Event
import Contact
import pickle
def saveObj(filename, obj):
    with open(filename, 'wb') as output:
    pickle.dump(obj,output, pickle.HIGHEST_PROTOCOL)
    print("SAVED")

def loadObj(filename, obj):
    with open(filename, 'rb') as input:
    obj = pickle.load(input)
    print("LOADED")

p1 = Person.Person("abcd",12,"ui")
p2 = Person.Person("Hah",123,"aaa")
c1 = Contact.Contact([p1,p2], "Wakanda", "12-23-54")
e1 = Event.Event([p1],"12-32-31")
e1.setTitle();
e1.setDescription();

c2 = Contact.Contact([p2],"Forever", "12-23-53")


print("1 for new user, 2 for existing user")
ipt = input("Write something but not exit!\n>>")
filename = ""
while (ipt!= "exit!"):
    if (ipt=="1"):
        print("1")
        idNumber = input("Insert id\n>> ")
        name = input("Inser name\n>> ")
        filename = str(idNumber)+".data"
        session = LoggedIn.User(idNumber,name)
        session.addStuff([e1],[c1,c2],[p1,p2])
        print(session.people)
        saveObj(filename,session)
        del session
    elif(ipt=="2"):
        print("2")
        session = LoggedIn.User(None,None)    
        loadObj(filename,session)
        print(session.people)
    ipt = input("Write something but not exit!\n>>")

The return I'd like would be equal to when I use option 1 and option 2. But instead it's like this:

1 for new user, 2 for existing user
Write something but not exit!
>>1
1
Insert id
>> 12345678
Inser name
>> AAA
[<Person.Person object at 0x7fa8079c6908>, <Person.Person object at 0x7fa8079c6940>]
SAVED
Write something but not exit!
>>2
2
LOADED
[]
Write something but not exit!
>>

How can I fix this?

score 1 · Accepted Answer · answered Jan 11 '19 at 18:01

1

obj = pickle.load(input) doesn't change the value of the object you passed in via the obj parameter. Try using return.

def loadObj(filename):
    with open(filename, 'rb') as input:
        obj = pickle.load(input)
    print("LOADED")
    return obj

#later...

print("2")
session = loadObj(filename)
print(session.people)

answered Jan 11 '19 at 18:01

Kevin

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I feel dumb, somehow I thought I was passing a reference. This will serve as a reminder to people that might have had the same problem.. THAT'S NOT A REFERENCE! (I will thank you very much for the quick response) – DTek Jan 11 '19 at 20:00
It's a fairly common problem because Python doesn't appear to follow either pass-by-reference or pass-by-value, which many other languages adhere to. In reality it actually _is_ quite close to pass-by-reference: at the beginning of your original function, obj and session are referentially identical, which you can confirm by printing the `id()` of both of them. But the `obj = ...` assignment statement only changes the value of obj, leaving session untouched. – Kevin Jan 11 '19 at 20:12

How can I save all information of a python class to binary?

1 Answers1