How can I improve this code?

# A simple notebook application
import code_util as util
# defining a class
available_bookclasses = ('private', 'public', 'none')
class notebook:
    # Varibles
    book_name = ''
    book_class = available_bookclasses[2]
    item_name = ''
    book_code = util.assign_code()
    items_list = []
   
    def __init__(self,name):
        self.book_name = name
    def _get(self,items):
        if ((items < 0)):
            print ("Invalid number of items..")
       
        for i in range(items):
            self.item_name = input("Enter item name: ")
            self.items_list.append(self.item_name)
    def count(self):
        return (len(self.items_list))
    def show_summary(self):
        print ("Name of the stored book: %s\n" %(self.book_name))
        print ("Secret code: %d\n" %(self.book_code))
        print ("Printing items in the list...\n")

        for i in range(self.count()):
            print ("Items [%d]: %s\n" %(i,self.items_list[i]))
    def create_copy_code(self):
        return (self.book_code)
    def __str__(self):
        self.show_summary()

    def change_class(self,class_name):
        if class_name in available_bookclasses:
            self.book_class = class_name
        else:
            util.error("Search failed: %s\n" % class_name)

# Utility Module
import random
import math
import sys
def error(*arg):
    print ("Number of errors: %d\n" % len(arg))
    for i in range(len(arg)):
        print ("Error [%d]: %s\n" %(i,arg[i]),file = sys.stderr)

def assign_code():
    '''
        () -> int
        return the assigned number

        >> assign_code()
        10q0
        >> assign_code()
        547a4
    '''

    # Varibles used in the assign_code()
    value_to_use = [22,3,4,2,3,2,3,3,111,2232,44,323,90909,9,23]
    number_to_use = [1,2,3,42,5,3,5,3,4,3,32,4,2,2,4]
    assigned_code = '' # The end result

    big_number = number_to_use[0] # let big_number be the largest number
    big_value = value_to_use[0] # let big_value be the largest number

    try:
        for n in range(len(number_to_use)):
            if (number_to_use[n] > big_number):
                big_number = number_to_use[n]
        n_use = random.randint(0,big_number)
        n_use*=100
        for v in range(len(value_to_use)):
            if (number_to_use[v] > big_value):
                big_value = value_to_use[v] # Largest value
        # Making it more harder
        v_use = random.randint(0,big_value)
        v_use*=100
    except ValueError:
        error("Code Generation")

    if (n_use > v_use):
        v_use+=n_use


    assigned_code = int(math.sqrt(random.randint(n_use,v_use))) # Creating code...
    assigned_code = math.sqrt(assigned_code * 100 * 100)
   
    return (int(assigned_code))