Question

I am writing a program to add to and update an address book. Here is my code:

EDITED

import sys
import os

list = []

class bookEntry(dict):
    total = 0

    def __init__(self):
        bookEntry.total += 1
        self.d = {}

    def __del__(self):
        bookEntry.total -= 1
        list.remove(self)

class Person(bookEntry):
    def __init__(self, n):
        self.n = n
        print '%s has been created' % (self.n)

    def __del__(self):
        print '%s has been deleted' % (self.n)

    def addnewperson(self, n, e = '', ph = '', note = ''):
        self.d['name'] = n
        self.d['email'] = e
        self.d['phone'] = ph
        self.d['note'] = note

        list.append()

    def updateperson(self):
        key = raw_input('What else would you like to add to this person?')
        val = raw_input('Please add a value for %s' % (key))
        self.d[key] = val
def startup():
    aor = raw_input('Hello! Would you like to add an entry or retrieve one?')
    if aor == 'add':
        info = raw_input('Would you like to add a person or a company?')
        if info == 'person':
            n = raw_input('Please enter this persons name:')
            e = raw_input('Please enter this persons email address:')
            ph = raw_input('Please enter this persons phone number:')
            note = raw_input('Please add any notes if applicable:')

            X = Person(n)
            X.addnewperson(n, e, ph, note)
startup()

When I run this code I get the following error:

in addnewperson
    self.d['name'] = n
AttributeError: 'Person' object has no attribute 'd'

I have two questions:

UPDATED QUESTIONS
1. why isnt the d object being inherited from bookentry()?

I know this question/code is lengthy but I do not know where to go from here. Any help would be greatly appreciated.

Answer 1

1. The addnewperson shoud have ‘self’ as first argument; actually, the name doesn’t matter (‘self’ is just a convention), but the first argument represent the object itself. In your case, it’s interpreting n as the “self” and the other 3 as regular arguments.

2. ____del____ must not take arguments besides ‘self’.

Edit: BTW I spotted a few other problems in your example, that maybe you’re not aware of:

1) d in bookentry is a class member, not an instance member. It’s shared by all bookentry’s instances. To create an instance member, use:

class bookentry(dict):
    def __init__(self,n):
        self.d = {}
        # rest of your constructor

2) you’re trying to access d directly (as you would do in Java, C++ etc), but Python doesn’t support that. You must have a ‘self’ parameter in your methods, and access instance variables through it:

class person(bookentry):
    def foo(self,bar):
       self.d[bar] = ...

person().foo(bar)

Update: for the last problem, the solution is to call the super constructor (which must be done explicitly in Python):

class Person(bookEntry):
    def __init__(self, n):
        super(Person, self).__init__()
        self.n = n
        print '%s has been created' % (self.n)

A brief explanation: for people with background in OO languages without multiple inheritance, it feels natural to expect the super type constructor to be called implicitly, automatically choosing the most suitable one if no one is mentioned explicitly. However, things get messy when a class can inherit from two or more at the same time, for this reason Python requires the programmer to make the choices himself: which superclass constructor to call first? Or at all?

The behavior of constructors (and destructors) can vary wildly from language to language. If you have further questions about the life cycle of Python objects, a good place to start would be here, here and here.