title: Python CVXPY: Attribute Error - Parameter
body: <p>I'm attempting to use CVXPY in python to solve a linear programming problem that has a handful of constraints. I created a single list with all of the constraints listed but when it came to running the problem.solve(), it returned the following error:</p>
  <p>&quot;AttributeError: 'list' object has no attribute 'parameters'&quot;</p>
  <p>I believe it's referencing the constraints list I created, but I'm at a loss for how to rectify the issue.</p>
  <pre><code>import cvxpy as cvx
  import numpy as np
  
  p = cvx.Variable(shape=(3,1), name=&quot;p&quot;)
  f = cvx.Variable(shape=(6,1), name=&quot;f&quot;)
  theta = cvx.Variable(shape=(6,1), name=&quot;theta&quot;)
  
  r = np.array([16, 20, 8])
  objective = cvx.Minimize(cvx.matmul(r,p))
  
  A = np.array([[1,0,0,0,0,1],[0,1,1,0,0,0],[0,0,0,1,1,0]])
  B = np.array([[1,0,0],[0,1,0],[0,0,1]])
  constraint_genflow = [cvx.matmul(A,f)==cvx.matmul(B,p)]
  
  C = np.array([[1,1,0,0,0,0],[0,0,1,1,0,0],[0,0,0,0,1,1]])
  D = np.array([[-110],[-65],[-205]])
  constraint_demandflow= [cvx.matmul(C,f)==D]
  
  E = np.array([[1,0,0,0,0,0],[0,1,0,0,0,0],[0,0,1,0,0,0],[0,0,0,1,0,0],[0,0,0,0,1,0],[0,0,0,0,0,1]])
  F = np.array([[-100],[-110],[-50],[-80],[-60],[-40]])
  G = np.array([[100],[110],[50],[80],[60],[40]])
  constraint_flowlimit1 = [cvx.matmul(E,f)&lt;=G]
  constraint_flowlimit2 = [cvx.matmul(E,f)&gt;=E]
  
  H = np.array([[1,0,0],[0,1,0],[0,0,1]])
  I = np.array([[20],[20],[10]])
  J = np.array([[200],[150],[150]])
  constraint_genpower1 = [cvx.matmul(H,p)&lt;=J]
  constraint_genpower2 = [cvx.matmul(H,p)&gt;=I]
  
  K = np.array([[11.6,-11.6,0,0,0,0],[0,5.9,-5.9,0,0,0],[0,0,13.7,-13.7,0,0],[0,0,0,9.8,-9.8,0],[0,0,0,0,5.6,-5.6],[-10.5,0,0,0,0,10.5]])
  L = np.array([[100],[110],[50],[80],[60],[40]])
  constraint_nodalpot = [cvx.matmul(K,theta)==L]
  
  constraints = [constraint_nodalpot, constraint_genpower1, constraint_genpower2, constraint_flowlimit2, constraint_flowlimit1, constraint_genflow, constraint_demandflow] 
  
  problem = cvx.Problem(objective, constraints)
  solution = problem.solve()
  print(solution)
  
  ---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  &lt;ipython-input-120-05b45a639232&gt; in &lt;module&gt;
        1 #Define the Problem and Solve
        2 problem = cvx.Problem(objective, constraints)
  ----&gt; 3 solution = problem.solve()
        4 print(solution)
  
  ~\Anaconda3\lib\site-packages\cvxpy\problems\problem.py in solve(self, *args, **kwargs)
      460         else:
      461             solve_func = Problem._solve
  --&gt; 462         return solve_func(self, *args, **kwargs)
      463 
      464     @classmethod
  
  ~\Anaconda3\lib\site-packages\cvxpy\problems\problem.py in _solve(self, solver, warm_start, verbose, gp, qcp, requires_grad, enforce_dpp, **kwargs)
      876             print(_HEADER)
      877 
  --&gt; 878         for parameter in self.parameters():
      879             if parameter.value is None:
      880                 raise error.ParameterError(
  
  ~\Anaconda3\lib\site-packages\cvxpy\utilities\performance_utils.py in _compute_once(self, *args, **kwargs)
       67         if key in cache:
       68             return cache[key]
  ---&gt; 69         result = func(self, *args, **kwargs)
       70         cache[key] = result
       71         return result
  
  ~\Anaconda3\lib\site-packages\cvxpy\problems\problem.py in parameters(self)
      334         params = self.objective.parameters()
      335         for constr in self.constraints:
  --&gt; 336             params += constr.parameters()
      337         return unique_list(params)
      338 
  
  AttributeError: 'list' object has no attribute 'parameters'
  </code></pre>
  <p>Any help would be greatly appreciated</p>