title: correcting unhashable type: 'dict_keys'
body: <p>try to find the max value in a nested dictionary, but showed unhashable type: 'dict_keys'error</p>
  
  <p>Suppose I have this dictionary:</p>
  
  <pre><code>d = {'A': {'a':2, 'b':2, 'c':0},
       'B': {'a':2, 'b':0, 'c':1}}
  </code></pre>
  
  <p>I want the code to return all the key(s) that contain maximum values within the dictionary (i.e. the maximum value in dictionary A is 2, and I want the code to return me the corresponding keys: 'a' and 'b')</p>
  
  <pre><code>['a','b']
  </code></pre>
  
  <p>here is the code I wrote:</p>
  
  <pre><code>max_value = max(d[Capital_Alph].values()))
  return [key for key, value in d[Capital_Alph].items()
          if value == max_value]
  </code></pre>