title: python time stamp convert to datetime without a year specified
body: <p>I have a csv file of a years worth of time series data where the time stamp looks like the code insert below. One thing to mention about the data its a <em>30 year averaged hourly weather data, so there isnt a year specified</em> with the time stamp.</p>
  
  <pre><code>Date
  01-01T01:00:00
  01-01T02:00:00
  01-01T03:00:00
  01-01T04:00:00
  01-01T05:00:00
  01-01T06:00:00
  01-01T07:00:00
  01-01T08:00:00
  01-01T09:00:00
  01-01T10:00:00
  01-01T11:00:00
  01-01T12:00:00
  01-01T13:00:00
  01-01T14:00:00
  01-01T15:00:00
  01-01T16:00:00
  01-01T17:00:00
  01-01T18:00:00
  01-01T19:00:00
  01-01T20:00:00
  01-01T21:00:00
  01-01T22:00:00
  01-01T23:00:00
  </code></pre>
  
  <p>I can read the csv file just fine:</p>
  
  <p><code>df = pd.read_csv('weather_cleaned.csv', index_col='Date', parse_dates=True)</code></p>
  
  <p>If I do a <code>pd.to_datetime(df)</code> this will error out:
  <code>ValueError: to assemble mappings requires at least that [year, month, day] be specified: [day,month,year] is missing</code></p>
  
  <p>Would anyone have any tips to convert my df to datetime? </p>