how to load objects from json file

I am trying to load simple objects from the json file. But i am getting error in it. below is my code and also the data in json format in db.txt file. I am calling the getAll() function of model.py from some other class.

file: model.py

import simplejson

class Person(object):
    def __init__(self, first_name = None, last_name = None):
        self.first_name = first_name
        self.last_name = last_name

    def name(self):
        return ("%s %s"%(self.first_name, self.last_name))

    @classmethod
    def getAll(self):
        database = open('db.txt', 'r')
        result = []
        json_list = simplejson.loads(database.read())
        print("json list {}".format(json_list))
        for item in json_list:
            print("item {}".format(item))
            print("type of item {}".format(type(item)))
            item = simplejson.loads(item)
            person = Person(item['first_name'], item['last_name'])
            result.append(person)
        return result

file: db.txt

[
    {
        "first_name":"first name",
        "last_name":"last name"
    },
    {
        "first_name":"first name 2",
        "last_name":"last name 2"
    }
]

ERROR (output):

json list [{'first_name': 'first name', 'last_name': 'last name'}, {'first_name': 'first name 2', 'last_name': 'last name 2'}]
item {'first_name': 'first name', 'last_name': 'last name'}
type of item <type 'dict'>
...
...
item = simplejson.loads(item)
...
...
KeyError: 0