title: Unable to update dictionary
body: <p>I am facing this problem while trying to code a Sudoku solver (with some parts referencing to <a href="http://norvig.com/sudoku.html" rel="nofollow">http://norvig.com/sudoku.html</a>)</p>
  
  <p>Here's the code I have made so far with reference to the above URL.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>puzzle = '003198070890370600007004893030087009079000380508039040726940508905800000380756900'
  cell = '123456789'
  cell_break = ['123','456','789']
  
  
  def generate_keys(A, B):
    "Cross product of elements in A and elements in B."
    return [a+b for a in A for b in B]
  
  #print generate_keys(cell,cell)
  
  def dict_puzzle(puzzle,cell):
    'Making a dictionary to store the key and values of the puzzle'
    trans_puzzle = {}
    key_list = generate_keys(cell,cell)
    i=0
    for x in puzzle:
      trans_puzzle[str(key_list[i])] = x
      i = i + 1
      return trans_puzzle
  
  dict_puzzle(puzzle,cell)['11'] = 'die'
  print dict_puzzle(puzzle,cell)['11']</code></pre>
  </div>
  </div>
  </p>
  
  <p>for the last 2 lines of the code, I tried to mutate the dictionary but to no avail. It just returns me 0, which is the original value. (i.e the mutation wasnt successful)</p>
  
  <p>I am not sure why is this happening :(</p>