Loading a saved dictionary (containing objects as values) from a file using pickle

Question

I am currently trying to learn Python and having learned the basics I decided to try to make an address book program. I am having trouble loading the contacts after they have been saved though. Here's what I have so far,

import pickle

contacts = {}

class Contact:
    def __init__(self, name, phone, address):
        self.name = name
        self.phone = phone
        self.address = address

Name = input('Contacts Name - ')
Phone = input('Phone Number - ')
Address = input('Address - ')

contacts[Name] = Contact(Name, Phone, Address)

with open('SaveFile', 'wb') as f:
    pickle.dump(contacts, f)

this all seems to work fine and the contacts dictionary is saved but when I try to load the contacts back after I have cleared the dictionary it does not work for some reason,

def load():
    with open('SaveFile', 'rb') as f:
        contacts = pickle.load(f)

I don't get an error message but the dictionary stays empty. Any help with this would be much appreciated!

Answer 1

Variables have scope. The contacts variable you assigned to within the load function has no relationship to the contacts you defined as a global variable. The simplest solution would be to make your function return the newly loaded contacts, letting you replace the existing dictionary:

def load_contacts():
    with open('SaveFile', 'rb') as f:
        new_contacts = pickle.load(f)

    return new_contacts

...

contacts = load_contacts()

If you do want to directly access the global contacts variable from within the load function, you can use the global keyword to tell Python that you're referring to contacts from the global scope:

def load():
    global contacts

    with open('SaveFile', 'rb') as f:
        contacts = pickle.load(f)

You could also avoid assigning to your global contacts and instead modify it:

def load():
    contacts.clear()

    with open('SaveFile', 'rb') as f:
        new_contacts = pickle.load(f)

    contacts.update(new_contacts)

The difference in the last example is that you're directly working with the object referred to by contacts .

Answer 2

尝试使用以下内容：

pickle.load(open("SaveFile", 'rb'))