title: "Not enough values to unpack" when iterating over dictionary of dictionaries
body: <p>I'm getting a value error <code>Not enough Values to unpack. Expected 3, got 2</code> when turning a dictionary into a list of tuples via a list comprehension.</p>
  
  <pre class="lang-py prettyprint-override"><code># Link MPNs to sales reps
  sam_parts = {}
  for row in plmdata:
      mpn,sam = row[5],row[24]
      mpn_heat = heatscores[mpn]
      if sam not in sam_parts:
          sam_parts[sam] = {mpn:mpn_heat}
      elif mpn not in sam_parts[sam]:
          sam_parts[sam][mpn] = mpn_heat
  
  # Convert sam_parts to list of tuples
  clean_parts = [(sam,mpn,mpn_heat) for sam,mpn,mpn_heat in sam_parts.items()]
  </code></pre>
  
  <p>The offending list comprehension is towards the bottom. I included code for the dictionary just in case. I'm sure there's a straightforward solution here that I'm just not seeing, but I need a fresh pair of eyes! Thanks in advance.</p>