Brute-Force Knapsack Printout

Question

I"m using combinations to show all total subsets of items possible within a knapsack, So if I had like 10 items, with varying value and weight It'd show all combinations of the items, the total weights which is in the second spot in the tuple (Id,Weight,Val) and the total values, my issue is I'm getting a tuple index out of range error.

#Knapsack

from random import *
from itertools import *

#Creates List of Items, using N for Num of Items
#Weightmax for the max range of weights
#Valmax of max value range
#Each Item has a Id, Weight and Value.
#Represented as a tuple. [(Id,Weight,Value)]
def item_list(n,weightmax,valmax):

    items = []
    for i in range(1,n+1):
        items.append((i,randrange(1,weightmax),randrange(1,valmax)))
    return items
#----------------------------------------------------
#Is the Sack, Takes Items as a parameter, and Capacity
#Purpose is to find and print all possible combinations that
#Will fit in the sack,then print which subset has the best
#weight for value mix.
def knapsack(items,capacity):
    sack = items
    subs = []
    print("------------------------------")
    print("Subset,","     |      ", "Total Weight", "     |     ", "Total Value")
    for i in range(len(sack)+1):
        print(i)
        for j in combinations(items, i):
            subs.append(j)
            print(j,"   |   ",j[i][1],"   |   ",j[i][2])

#------------------------------------    
#Main, Asks for UserInput and allows you
#to re-enter mistypes.
def main():
    choices = False 
    print("Welcome to the Knapsack Filler!")
    print("Please Input the Following Parameters; ")
    while choices is False:
        knapcap = int(input("Enter Knapsack Max Capacity: "))
        maxweight = int(input("Enter Max Range for Weights: "))
        maxval = int(input("Enter Max Value Range for Weights: "))
        numitems = int(input("Number of Items you wish to generate: "))
        prompt= input("\n Y or N; Are you Sure about your Choices?: ")
        if prompt.lower() =="yes" or "y":
            choices = True
        else:
            pass
    knapsack(item_list(numitems,maxweight,maxval),knapcap)
main()

Error:

Traceback (most recent call last):
  File "C:\CS230\CS320_P2_Knapsack.py", line 54, in <module>
    main()
  File "C:\CS230\CS320_P2_Knapsack.py", line 53, in main
    knapsack(item_list(numitems,maxweight,maxval),knapcap)
  File "C:\CS230\CS320_P2_Knapsack.py", line 31, in knapsack
    print(j,"   |   ",j[i][1],"   |   ",j[i][2])
IndexError: tuple index out of range

Sample Input:

Welcome to the Knapsack Filler!
Please Input the Following Parameters; 
Enter Knapsack Max Capacity: **30**
Enter Max Range for Weights: **10**
Enter Max Value Range for Weights: **10**
Number of Items you wish to generate: **3**

 Y or N; Are you Sure about your Choices?: Y
------------------------------
Subset,      |       Total Weight      |      Total Value
0

Answer 1

This is a difficult question to answer because the problem you're having arises from conceptual, but also architectural difficulties in your code. I've rewritten your code in a form similar to how I would have done it myself in the hopes that seeing "good code" will help you figure out where you may have gone wrong.

A few of the major changes I've made include:

• Introducing a powerset function, since this is the list of items you're trying to generate
• Introducing an Item class to make id, weight, and value clearly accessible
• Introducing a Sack class to abstract the details of finding a subset of items' weight and value

If you don't know how to use classes yet, they're really good things to know, as the code below demonstrates.

Code

#!/usr/bin/env python3

import random
import itertools

class Item:
  def __init__(self, id, weight, value):
    self.id     = id
    self.weight = weight
    self.value  = value

class Sack:
  def __init__(self, items):
    self.items = items

  def weight(self):
    return sum([x.weight for x in self.items])

  def value(self):
    return sum([x.value for x in self.items])

  def ids(self):
    return ', '.join([str(x.id) for x in self.items])

  def __repr__(self): #What gets shown when you call the print function
    return "{0:10} {1:10}   {2}".format(self.weight(), self.value(), self.ids())


def powerset(iterable):
  """
    powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)

    Source: https://docs.python.org/2/library/itertools.html
  """
  s = list(iterable)
  return itertools.chain.from_iterable(itertools.combinations(s, r) for r in range(len(s)+1))



def item_list(n,weightmax,valmax):
  """
    Creates a list of randomly generated items

    Arguments:
      n          Number of items to have in the sack
      weightmax  Weights are generated in the range [1,weightmax]
      valuemax   Values are generated in the range [1,valuemax]

    Returns:
      A list of [(Id,Weight,Value), (Id,Weight,Value), ...]
"""
  items = []
  for i in range(1,n+1):
    items.append(Item(id=i, weight=random.randint(1,weightmax), value=random.randint(1,valmax)))
  return items



def knapsack(items,capacity):
  """Find and print all the combinations of items that will fit into the sack.
     Also print the most valuable combination.

    Arguments:
      items      A list of items generated by item_list()
      capacity   The maximum weight the knapsack can hold
  """
  print("------------------------------")
  print("{0:>10} {1:>10}   {2}".format("Weight","Value","Subset"))
  subsets_that_fit = []
  for sackitems in powerset(items):
    sack = Sack(sackitems)
    if sack.weight()>capacity:
      continue
    print(sack)
    subsets_that_fit.append(sack)
  best = max(subsets_that_fit, key=lambda x: x.value())
  print("Best")
  print(best)



def main():
  choices = False 
  print("Welcome to the Knapsack Filler!")
  print("Please Input the Following Parameters; ")
  while choices is False:
    knapcap   = int(input("Enter Knapsack Max Capacity: "))
    maxweight = int(input("Enter Max Range for Weights: "))
    maxval    = int(input("Enter Max Value Range for Weights: "))
    numitems  = int(input("Number of Items you wish to generate: "))
    prompt    = input("\n Y or N; Are you Sure about your Choices?: ")
    if prompt.lower() =="yes" or "y":
      choices = True
    else:
      pass

  knapsack(item_list(numitems,maxweight,maxval),knapcap)

main()