title: How to return a dictionary using field function in Odoo
body: <p>I got an error in my field function.
  In my function, I want to return a float value from my variable <code>total</code>. And I already searched it and I found an answer <a href="https://stackoverflow.com/questions/27628039/valueerror-dictionary-update-sequence-element-0-has-length-1-2-is-required">here</a> but still I don't understand the explanation.
  Here's my error.</p>
  
  <pre><code>ValueError: dictionary update sequence element #0 has length 1; 2 is required
  </code></pre>
  
  <p>Here is my code.</p>
  
  <pre><code>@api.multi
  @api.depends('total_eec', 'total_tec')
  def _consumption_actual_value(self):
      res = {}
      total = 0.0
      for i in self:
          total = i.total_eec + i.total_tec
          res[i.id] = total
      return res
  
  _columns = {'consumption_actual': fields.function(_consumption_actual_value, string='Consumption (kWh) Actual'), # TEC + EEC}
  </code></pre>
  
  <p>Please help.</p>