title: Entire column filled in a list in python
body: <p>Ok, this is bizarre. I don't understand and it's getting extremely frustrating.</p>
  
  <ol>
  <li>I declare and array (list)</li>
  <li>I initiate the first row with strings (stock symbols)</li>
  <li>I populate the rest with zeros for the required number of trading days.</li>
  <li><p>The I want to populate certain elements of the 'positions' matrix with a number for stocks to be purchased or sold on that day. And instead of populating only the one element, the entire column populates.</p>
  
  <pre><code># Initiating position matrix
  positions = []
  # Initiating a row of zeros (to fill position matrix later)
  empty_row = []
  # Symbols is a list of symbols that will be traded.
  for symbol in symbols:
      empty_row.append(0)
  
  # First row of positions will be symbols
  positions.append(symbols)
  
  # All other rows will be empty_rows
  for day in timestamps:
      positions.append(empty_row)
  </code></pre>
  
  <p>Then I will determine what element of "positions" I need to populate. Let's say the element on the 10th row and 1st column (indexing from zero). So i do:</p>
  
  <p>positions[10][1] = 100</p>
  
  <p>The result I get is that the ENTIRE column 1 is full of 100s. Not just the element. What am I doing wrong?</p></li>
  </ol>