input: Write a function to calculate the maximum possible revenue from the items with given weights and values using a knapsack algorithm. The function should take three parameters: a list of weights, a list of values, and the total capacity of the knapsack, and return the maximum revenue possible.
  
  def knapsack(weights, values, W):
      n = len(weights)
      K = [[0 for x in range(W+1)] for x in range(n+1)]
      for i in range(n+1):
          for w in range(W+1):
              if i==0 or w==0:
                  K[i][w] = 0
              elif weights[i-1] <= w:
                  K[i][w] = max(values[i-1] + K[i-1][w-weights[i-1]],  K[i-1][w])
              else:
                  K[i][w] = K[i-1][w]
      return K[n][W]
  
  assert knapsack([2, 1, 3], [4, 2, 3], 5) == 7
  assert knapsack([3, 2, 1, 4], [5, 4, 3, 6], 5) == 9
  assert knapsack([2, 2, 2], [3, 4, 5], 3) == 5
  assert knapsack([1, 2, 3], [1, 2, 3], 0) == 0
  assert knapsack([], [], 5) == 0
output: def knapsack(weights, values, W):
      n = len(weights)
      K = [[0 for x in range(W+1)] for x in range(n+1)]
      for i in range(n+1):
          for w in range(W+1):
              if i==0 or w==0:
                  K[i][w] = 0
              elif weights[i-1] <= w:
                  K[i][w] = max(values[i-1] + K[i-1][w-weights[i-1]],  K[i-1][w])
              else:
                  K[i][w] = K[i-1][w]
      return K[n][W]