title: Python34: Using Dictionary Comprehension to Copy Values form one list of dictionaries to another
body: <p>I am writing a script to process data so I have a list containing dictionaries with calculated values. Once I calculate new ones I want to append the appropriate dictionary with new entries. </p>
  
  <p>I know I could do this with list or np array, but I want to learn how to use dictionaries. I also just started using list comprehension so I want to get a better understanding on how to use it appropriately. So making life hard on myself. </p>
  
  <p>Here is simplified examples.</p>
  
  <p>I calculate values and place them in the dictionary, which then goes in a list to correspond for each entry.</p>
  
  <pre><code>A=[{'low':1},{'low':2}]
  print(A)
  [{'low': 1}, {'low': 2}]   # entry 0 corresponds to sample 1 and the next to sample 2
  
  B=[{'hi':1},{'hi':2}]
  print(B)
  [{'hi': 1}, {'hi': 2}]   # entry 0 corresponds to sample 1 and the next to sample 2
  
  C=[{}]*len(A)   # initialize list to contain a dictionary for each sample. Each dictionary will receive the corresponding values copied from A and B
  print(C)
  [{}, {}]
  </code></pre>
  
  <p>Now I try to use dictionary comprehensions</p>
  
  <pre><code>{C[x].update(A[x]) for x in range(len(A))}
  print(C)
  [{'low': 2}, {'low': 2}]
  </code></pre>
  
  <p>The results is not what I expected. I want something like this:</p>
  
  <pre><code>[{'low':1,'high':1},{'low':1,'high':1}]
  </code></pre>
  
  <p>What am I not understanding here...</p>
  
  <p>Thanks</p>