title: how can I generate a list of days by known months
body: <p>I just start learning python for few weeks and now have a problem with datetimes</p>
  
  <p>I generate a list like this </p>
  
  <pre><code>datetime.date(1991, 11, 1),
  datetime.date(1991, 12, 1),
  datetime.date(1992, 1, 1),
  ...
  datetime.date(2017, 10, 1),
  datetime.date(2017, 11, 1),
  datetime.date(2017, 12, 1)]
  </code></pre>
  
  <p>which the time step is month
  and I would like to use it to create a list like this</p>
  
  <pre><code>datetime.date(1991, 11, 1),
  datetime.date(1991, 11, 2),
  datetime.date(1991, 11, 3),
  ...
  datetime.date(2017, 12, 29),
  datetime.date(2017, 12, 30),
  datetime.date(2017, 12, 31)]
  </code></pre>
  
  <p>which the time step become days and the last day is the end of the month.</p>
  
  <p>I use some way such as calculate monthrange and then generate a new list from the starting day, but the code seems lengthy and not so good.</p>
  
  <p>Do anyone have a better way to solve this? thanks for advance! </p>