title: Python - for cycle in a list of lists
body: <p>I'm trying to create a list with the number of days of each month between 1901 and 2000, but I can't manage to change the values properly.
  Here's my code:</p>
  
  <pre><code>year = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
  period = [year] * 100
  
  for i in range(1901, 2001):
      if i % 4 == 0 and i % 100 != 0:
          period[i-1901][1] = 29
  
  period[99][1] = 29
  print period
  </code></pre>
  
  <p>When I execute it, the list that I get has 29 as second entry for every year, which I obviously do not want. What am I doing wrong? Thanks.</p>