Create List Object Class in Python

Question

It is a basic question. I am trying the following code:

class SMS_store:

def __init__(self):
    self=[]    #probably something is wrong here

def add_new_arrival(self,from_number,time_arrived,text_of_SMS):
    self.append([False,from_number,time_arrived,text_of_SMS])    #append list to self list
    self[len(self)-1]=tuple(self[len(self)-1])

def message_count(self):
    return len(self)

my_inbox=SMS_store()
my_inbox.add_new_arrival('01234','9:37 AM','How are you?')

But I get the following error:

>>> 
Traceback (most recent call last):
  File "C:\Users\Arnob\Desktop\New Text Document.py", line 15, in <module>
    my_inbox.add_new_arrival('01234','9:37 AM','How are you?')
  File "C:\Users\Arnob\Desktop\New Text Document.py", line 8, in add_new_arrival
    self.append([False,from_number,time_arrived,text_of_SMS])    #append list to self list
AttributeError: 'SMS_store' object has no attribute 'append'
>>>

What is wrong in my code?

Answer 1

You can subclass list like this

class SMS_store(list):

    def add_new_arrival(self, from_number, time_arrived, text_of_SMS):
        self.append((False, from_number, time_arrived, text_of_SMS))    #append tuple to self

    def message_count(self):
        return len(self)

Notice there is no need for __init__ unless you wish to do something extra there.

You don't need to append a list and then turn it into a tuple, you can create the tuple directly with () instead of []

Answer 2

If you want to inherit from list, use the following:

class SMS_store(list):
               ^^^^^^

and remove that assignment to self from the __init__ method.

That said, you might want to simply have a named attribute containing the list:

class SMS_store(object):

   def __init__(self):
      self.messages = []

   def add_new_arrival(self, from_number, time_arrived, text_of_SMS):
      self.messages.append((False,from_number,time_arrived,text_of_SMS))

   def message_count(self):
      return len(self.messages)

my_inbox = SMS_store()
my_inbox.add_new_arrival('01234','9:37 AM','How are you?')

As far as representing actual messages, this sounds like a good use case for namedtuple. It's just like a tuple, but allows access to fields by name. Here is a quick illustration:

import collections

SMS = collections.namedtuple('SMS', 'from_number time_arrived text_of_SMS')

sms = SMS(from_number='01234', time_arrived='9:37 AM', text_of_SMS='How are you?')
print sms.text_of_SMS

Answer 3

You need to still create a normal variable name, just put self. as a prefix:

self.mylist = []

To access it, you do something like:

self.mylist.append(n)

Or:

self.mylist[3] = 'hi'

You're actually overriding self. You don't want to do that.