Originally posted by: Zoubeir

I have a simple constraints of the form

x_{kn} <= y_n for all k, n

I need to write this in Python. I did this

import cplex
x = []
y = []
xy = []

for n 
in 
range(
N):
    yname = 
"y_" + 
str(n)
    y.append(yname) 
for k 
in 
range(
K):
        xname = 
"x_" + 
str(k) + 
str(n)
        
x.append(xname)
xy.append(
x)
xy.append(y)
prob.variables.add(
names=y, 
lb=[
0] * 
len(y), 
ub=[
1] * 
len(y), 
types=[
"B"] * 
len(y), 
obj=[
1] * 
len(y))
prob.variables.add(
names=
x, 
lb=[
0] * 
len(
x), 
ub=[
1] * 
len(
x), 
types=[
"B"] * 
len(
x))

for k 
in 
range(
K):    
   for n 
in 
range(
N):
        prob.linear_constraints.add(
lin_expr=[cplex.SparsePair(
x[n][k]-y[n], [
1])], 
senses=[
"L"], 
rhs=
0)

I get an error message

prob.linear_constraints.add(lin_expr=[cplex.SparsePair(x[n][k]-y[n], [1])],
TypeError: unsupported operand type(s) for -: 'str' and 'str'

Maybe take a look at the various Python examples that are shipped with CPLEX and at the reference manual.

The correct code to add your constraint is

prob.linear_constraints.add(lin_expr = [cplex.SparsePair([ x[n][k], y[n] ], [1, -1])], senses = ['L'], rhs = [0.0])