Attribute Error for NQueensProblem in search.ipynb

[s-m-sharjeel]

AttributeError: 'NQueensProblem' object has no attribute 'graph' in cell [70] of search.ipynb:

%%timeit
depth_first_tree_search(nqp)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[70], line 1
----> 1 get_ipython().run_cell_magic('timeit', '', 'depth_first_tree_search(nqp)\n')

File ~\AppData\Local\Programs\Python\Python311\Lib\site-packages\IPython\core\interactiveshell.py:2543, in InteractiveShell.run_cell_magic(self, magic_name, line, cell)
   2541 with self.builtin_trap:
   2542     args = (magic_arg_s, cell)
-> 2543     result = fn(*args, **kwargs)
   2545 # The code below prevents the output from being displayed
   2546 # when using magics with decorator @output_can_be_silenced
   2547 # when the last Python token in the expression is a ';'.
   2548 if getattr(fn, magic.MAGIC_OUTPUT_CAN_BE_SILENCED, False):

File ~\AppData\Local\Programs\Python\Python311\Lib\site-packages\IPython\core\magics\execution.py:1209, in ExecutionMagics.timeit(self, line, cell, local_ns)
   1207 for index in range(0, 10):
   1208     number = 10 ** index
-> 1209     time_number = timer.timeit(number)
   1210     if time_number >= 0.2:
   1211         break

File ~\AppData\Local\Programs\Python\Python311\Lib\site-packages\IPython\core\magics\execution.py:173, in Timer.timeit(self, number)
    171 gc.disable()
    172 try:
--> 173     timing = self.inner(it, self.timer)
    174 finally:
    175     if gcold:

File <magic-timeit>:1, in inner(_it, _timer)

Cell In[16], line 50, in depth_first_tree_search(problem)
     48 def depth_first_tree_search(problem):
     49     "Search the deepest nodes in the search tree first."
---> 50     iterations, all_node_colors, node = tree_depth_search_for_vis(problem)
     51     return(iterations, all_node_colors, node)

Cell In[16], line 9, in tree_depth_search_for_vis(problem)
      7 iterations = 0
      8 all_node_colors = []
----> 9 node_colors = {k : 'white' for k in problem.graph.nodes()}
     11 #Adding first node to the stack
     12 frontier = [Node(problem.initial)]

AttributeError: 'NQueensProblem' object has no attribute 'graph'