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I develop mathematical model using gurobi solver, in python.
I get the following error while running:

SyntaxError: Generator expression must be parenthesized if not sole argument

My constraint is: enter image description here

My code is: 

for s in S:
    m.addConstr(sum(x[s,s0,c,i] for s0 in S0 for c in C for i in D,s!=p) == 1,'C_3')
Mel
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Tahirov
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1 Answers1

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First of all, everything comes whenever you add that comma: ,s!=p.

I just emulated your code with a model I'm working on, and I obviously got the same error. Look around (e.g. if else in a list comprehension), and you will see that the only mistake you had was that the iterator within the generator wasn't well specified. That means, you had to use an if clause in order to achieve what you wanted:

for s in S:
    m.addConstr( 
     quicksum(x[s,s0,c,i] for s0 in S0 for c in C for i in D if s!=p) == 1,
      'C_3_'+str(s) )

By the way, as included in the code, you should use quicksum instead of sum. Furthermore, I would suggest to try changing the order of the iterators; in other words, it's not the same for a computer to enumerate a list of 5 elements 1000 times than to enumerate 5 times a list of 1000 elements, and this is something quite important in Python timing.

As a side note, I got into this question while looking for this: TypeError: unsupported operand type(s) for +: 'generator' and 'generator'

Andymt
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