Python - When to create a Class and when to create a Function

class, function, oop, python

Solution

Adding a contact is doing something, rather than being something, so it would make sense as a method/function rather than a class. I would suggest that your functionality should actually be in two separate places.

Creating a new contact from user input should be a class method of `Contact`:

class Contact(object):

    ...

    @classmethod
    def from_input(cls):
        firstName = input("First Name: ")
        lastName = input("Last Name: ")
        address = input("Address: ")
        telephone = input("Telephone: ")
        mobile = input("Mobile: ")
        email = input("Email: ")
        return cls(firstName, lastName, address, None, 
                   telephone, mobile, email, None)

Adding a new contact to the list of contacts should either be:

- An instance method of the e.g. `AddressBook` or `ContactList` class (or whatever you have holding the contact list); or

- A separate function if you don't have a class to hold the `Contact` instances.

For example:

class AddressBook(object):

    ...

    def add_contact(self, contact=None):
        if contact is None:
            contact = Contact.from_input()
        self.contacts.append(contact)

Now your UI can create a `Contact` and pass it straight to `address_book.add_contact()`.

Problem

Right, so I'm trying to create a Contacts application using Python OOP. I'm fairly new to OOP and still trying to get my head around the concepts. I understand that a Class is a blueprint for all objects. I like to think of a Class as an entity and each Object is a record of that entity. I am from a Database background so that's why I interpret it like this, feel free to correct me. Anyways, in the Contacts app I'm making I've created the Class `Contacts` as outlined below: ``` class Contacts(): def __init__(self, firstName, lastName, address, groupType, telephone, mobile, email, photoField): self.firstName = firstName self.lastName = lastName self.address = address self.groupType = groupType self.telephone = telephone self.mobile = mobile self.email = email self.photoField = photoField def showDetails(self): print("First Name:\t", self.firstName) print("Last Name:\t", self.lastName) print("Address:\t", self.address) print("Telephone:\t", self.telephone) print("Mobile:\t", self.mobile) print("Email:\t", self.email) ``` Now, if I want to add contacts through the Contacts class into the list I'm using to store each contact object, do I have to create an `AddContacts` class, or do I create a function instead? I don't know if I'm putting my question across well enough for you to understand what I mean? What I guess I'm trying to say is that adding contacts is a process and if you look at it from a database point of view you wouldn't create a table called "tbl_AddContacts" since you would do that via a query or a stored procedure, so in my view I would define adding contacts being a function. But asking my colleague who does C# programming he says that adding contacts should be defined by a Class. This is a confusing concept for me, especially since I don't understand how I would link the `AddContacts` class with the `Contacts` class, or even how to define an `AddContacts` class in the first place!. Here is the function I defined for adding contacts: ``` def addContacts(): firstName = input("First Name: ") lastName = input("Last Name: ") address = input("Address: ") telephone = input("Telephone: ") mobile = input("Mobile: ") email = input("Email: ") print("\n") contact = Contacts(firstName, lastName, address, None, telephone, mobile, email, None) contactsList.append(contact) pickle.dump(contactsList, open("save.p", "wb")) ``` Please help me out, since I will turning this into a GUI application (uni assignment).

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