CODEWITHSUNDEEP
or-toolscp-sat
pofferbacco
pofferbacco

Reputation: 155

Google OR-Tools library: Type Error GetOrMakeIndex

I'm studying the google OR-Tools library and I came across this problem that I can't understand. First of all, I get the same error if I copy and paste the code from the nqueens example in the official guide.

I propose as an example the classic n-queens problem:

def main(board_size):

   #1) Declare CP-SAT model
   model = cp_model.CpModel()

   #2) Create the variables
   # queens[j]=i --> j = colonna, i (valore) = riga
   queens = [model.NewIntVar(0, board_size - 1, "queens%i" %i) for i in range(board_size)]

   #3) Constraints
   # Row constraint
   model.AddAllDifferent(queens)

   # Diagonal constraint
   model.AddAllDifferent([queens[j] - j for j in range(board_size)])
   model.AddAllDifferent([queens[j] + j for j in range(board_size)])

   #4) Call the solver and display the results
   solver = cp_model.CpSolver()
   solution_printer = NQueenSolutionPrinter(queens)
   solver.parameters.enumerate_all_solutions = True
   solver.Solve(model, solution_printer)

if __name__ == '__main__':
   size = 4
   if len(sys.argv) > 1:
      size = int(sys.argv[1])
   main(size)

The console gives me this error:

Traceback (most recent call last):

File "C:\Users\W\.spyder-py3\temp.py", line 90, in <module>
  main(size)

File "C:\Users\W\.spyder-py3\temp.py", line 67, in main
  model.AddAllDifferent([queens[j] - j for j in range(board_size)])

File "C:\ProgramData\Anaconda3\lib\site-packages\ortools\sat\python\cp_model.py", line 926, in AddAllDifferent
  [self.GetOrMakeIndex(x) for x in variables])

File "C:\ProgramData\Anaconda3\lib\site-packages\ortools\sat\python\cp_model.py", line 926, in <listcomp>
  [self.GetOrMakeIndex(x) for x in variables])

File "C:\ProgramData\Anaconda3\lib\site-packages\ortools\sat\python\cp_model.py", line 1583, in GetOrMakeIndex
  raise TypeError('NotSupported: model.GetOrMakeIndex(' + str(arg) +

TypeError: NotSupported: model.GetOrMakeIndex((queens0))

So, looking at the definition of the GetOrMakeIndex method:

def GetOrMakeIndex(self, arg):
    """Returns the index of a variable, its negation, or a number."""
    if isinstance(arg, IntVar):
        return arg.Index()
    elif (isinstance(arg, _ProductCst) and
          isinstance(arg.Expression(), IntVar) and arg.Coefficient() == -1):
        return -arg.Expression().Index() - 1
    elif isinstance(arg, numbers.Integral):
        cp_model_helper.AssertIsInt64(arg)
        return self.GetOrMakeIndexFromConstant(arg)
    else:
        raise TypeError('NotSupported: model.GetOrMakeIndex(' + str(arg) +

it comes to my mind that the variable does not recognise the type of variable it receives as an argument. Any idea how to solve the problem?

Upvotes: 1

Views: 524

Answers (1)

Laurent Perron
Laurent Perron

Reputation: 11034

This requires a recent version of the library. Which one are you using ?

Upvotes: 1

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