`#!/usr/bin/env python3

-- coding: utf-8 --

"""
Created on Tue May 22 22:02:13 2018

Taken from: https://github.com/fzsun/cutstock-gurobi

@author: Fangzhou Sun

This code solves the following cutting stock model:

Master problem:
min \sum_{p in P} x_p
s.t. \sum_{p in P} patterns_{ip} * x_p ≥ d_i, for i in I
x_p ≥ 0 and integer, for p in P

Subproblem:
min 1 - \sum_{i in I} price_i * use_i
s.t. \sum_{i in I} w_i * use_i ≤ W_roll
use_i ≥ 0 and integer, for i in I

x_p: number of times pattern p is used
price_i: dual of constraint i in the master problem
use_i: number of item i's in a new pattern
"""

import numpy as np
import logging
from itertools import count
import sys
'''
The following path should be adjusted to where gurobipy.py is located on
your system for the specific version of python that you will be using
'''
sys.path.insert(1,'C:/gurobi902/win64/python36/lib')
from gurobipy import *

def keyboard_terminate(model, where): # Enable pause m.optimize() by 'ctrl + c'
try:
pass
except KeyboardInterrupt:
model.terminate()

logger = logging.getLogger(name) # Set up logger
if not logger.hasHandlers():
logger.addHandler(logging.StreamHandler())
file_handler = logging.FileHandler('RunLog.log')
formatter = logging.Formatter(
fmt='%(asctime)s %(filename)s:%(levelname)s - %(message)s',
datefmt='%Y-%m-%d %H:%M:%S')
file_handler.setFormatter(formatter)
logger.addHandler(file_handler)
logger.setLevel(logging.DEBUG)
logger.info('Begin')

=========================== Parameters ======================================

np.random.seed(1)
TOL = 1e-6
W_roll = 100 # roll width
I = list(range(5)) # item set
w = np.random.randint(1, 50, len(I)).tolist() # width of each item
d = np.random.randint(1, 50, len(I)).tolist() # demand of each item
patterns = np.diag([W_roll // w[i] for i in I]).tolist() # initial patterns

========================= Master Problem ====================================

m = Model('cutstock')
m.ModelSense = GRB.MINIMIZE
x = m.addVars(len(patterns), obj=1, vtype='C', name='x')
c1 = m.addConstrs((patterns[i][i] * x[i] >= d[i] for i in I), name='c1')

======================= Subproblem and Iteration ============================

for iter_count in count():
m.write('master_problem.lp')
m.optimize(keyboard_terminate)
price = [c1[i].pi for i in I]
print(f'Price = {price}')

sp = Model('subproblem') # Subproblem
sp.ModelSense = GRB.MAXIMIZE
use = sp.addVars(I, obj=price, vtype='I', name='use')
c2 = sp.addConstr(quicksum(w[i]*use[i] for i in I) <= W_roll)
sp.write('subproblem.lp')
sp.optimize(keyboard_terminate)
min_rc = 1 - sp.objVal
if min_rc < -TOL:
    patterns.append([int(use[i].x) for i in I])
    logger.info(f'min reduced cost = {min_rc:.4f};'
                f' new pattern: {patterns[-1]}')
    x[iter_count+len(I)] = m.addVar(obj=1, vtype='C',
                                  column=Column(patterns[-1], c1.values()))
else:
    break

====================== Relaxed Model Result =================================

logger.info(f'min reduced cost = {min_rc:.4f} ≥ 0')
relaxed_result = [f'{v.x:.4f} * {patterns[p]}' for
p, v in enumerate(m.getVars()) if v.x > TOL]
relaxed_result.insert(0, f'Relaxed result = {m.objVal:.4f} rolls')
logger.info('\n\t'.join(relaxed_result))

====================== Integer Model Result =================================

m.setAttr('VType', x.values(), 'I'*len(x))
m.write('master_problem.lp')
m.optimize(keyboard_terminate)
integer_result = [f'{int(v.x)} * {patterns[p]}' for
p, v in enumerate(m.getVars()) if v.x > TOL]
integer_result.insert(0, f'Integer result = {int(m.objVal)} rolls')
logger.info('\n\t'.join(integer_result))`

This generates the following error:
**File "C:\PythonTestCode\LinearProgramming\Gurobi\StockCutting_01.py", line 102, in
m.setAttr('VType', x.values(), 'I'*len(x))
File "C:\gurobi902\win64\python36\lib\gurobipy\gurobipy.pyd", line 1869, in gurobipy.Model.setAttr
File "C:\gurobi902\win64\python36\lib\gurobipy\gurobipy.pyd", line 281, in gurobipy.__settypedattrlist

builtins.ValueError: only single character unicode strings can be converted to Py_UCS4, got length 12**

Note, I am using Python 3.6.5 on a Windows 10 platform.