title: Python reverse list in iterator
body: <p>I am looking to create two dictionaries from a list of nested lists: </p>
  
  <pre><code>M = {index of list: list}
  
  N = {index of list: reversed list}
  </code></pre>
  
  <p>Example:</p>
  
  <p>For starters I have the following list:</p>
  
  <pre><code>L =  [[20, 56], [23, 24], [23, 12], [22, 21], [26, 48], [26, 24]]
  </code></pre>
  
  <p>so the end result would be:</p>
  
  <pre><code>M = {0: [56, 20], 1: [24, 23], 2: [12, 23], 3: [21, 22], 4: [48, 26], 5: [24, 26]}
  N = {0: [20, 56], 1: [23, 24], 2: [23, 12], 3: [22, 21], 4: [26, 48], 5: [26, 24]}
  </code></pre>
  
  <p>I have tried this out:</p>
  
  <pre><code>M = {}
  N = {}
  for index, pair in enumerate(L):
      M[index] = pair
      N[index] = pair.reverse()
  </code></pre>
  
  <p>but the result of this is:</p>
  
  <pre><code>M = {0: [56, 20], 1: [24, 23], 2: [12, 23], 3: [21, 22], 4: [48, 26], 5: [24, 26]}
  N = {0: [56, 20], 1: [24, 23], 2: [12, 23], 3: [21, 22], 4: [48, 26], 5: [24, 26]}
  </code></pre>
  
  <p>I have solved it by doing:</p>
  
  <pre><code>N[index] = pair[::-1]
  </code></pre>
  
  <p>but could someone please tell me why this is happening?</p>