Is there an xsum constraint function similar to python-mip in or-tools, which can constrain the total sum?

[Bob Michael]

Using xsum in python-mip can achieve something like this:

“model += xsum(x.var for x in group.items) >=1”

The sum cannot be greater than 1. Does or-tools have such a function?

[Laurent Perron]

You mean the sum must be greater or equal to 1. There are plenty of sample code in ortools/linear_solver/samples.

Should be with the linear solver python API

solver.Add(sum(..) >= 1)

Now, if you use the CP-SAT native API, 

You can write 

model.Add(sum(..) >= 1)

If all variables are literals (Boolean variables or their logical negation), you can also write 

model.AddAtLeastOne(list of literals).

Now, with CP-SAT,, you can also write indicator constraints

model.Add(linear equation).OnlyEnforceIf(b1, b2.Not())

Indicating that the linear equation should be enforced only if b1 is true and b2 is false. (This is an implication). 

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