title: TypeError: unsupported operand type(s) for +: 'tupledict' and 'float'
body: <p>I have a model to be optimized by gurobi/python interface. the model is called m.
  Bk is a continuous variable and t[0,j] is a value of a key in a dictionary, why Gurobi cannot add Bk to t[0,j].</p>
  <p>I get this error at the next constraint:</p>
  <pre><code>m.addConstrs((B[j] &gt;= Bk + t[0,j] - M*(1-xijk[k,0,j]) for j in N for k in K), '9')
  </code></pre>
  <p>I set the following input data:</p>
  <pre><code>ek=0
  lk = 25200
  K = [1,2]
  N = [ i for i in range(23)]
  Xijk = m.addVars(K,N,N, vtype= GRB.BINARY) 
  
  Bk = m.addVars(K, vtype=GRB.CONTINUOUS)
  B  = m.addVars(N ,vtype=GRB.CONTINUOUS)
  
  t = {(0, 0): 0.0, (0, 9): 0.0, (0, 1): 59.0, (0, 2): 471.0, (0, 3): 353.0, (0, 4): 529.0, (0, 5): 471.0, (0, 6): 412.0, (0, 7): 412.0, (0, 8): 412.0, (0, 10): 353.0, (0, 11): 59.0, (0, 12): 471.0 .........to (22,22):0.0}
  </code></pre>
  <p>Bk appears later in constraint# 16 as follows</p>
  <pre><code>m.addConstrs((Bk &gt;= ek for k in K), '16-')
  m.addConstrs((Bk &lt;= lk for k in K), '16')
  </code></pre>