title: Pandas, Python, data missing year column
body: <p>I have a dataframe that look like this...</p>
  <pre><code>        Date      Time    Meridiem    Day
    80    01-05   9:35:00   AM      Tuesday
    81    01-05   9:40:00   AM      Tuesday
    82    01-05   9:45:00   AM      Tuesday
    83    01-05   9:50:00   AM      Tuesday
    84    01-05   9:55:00   AM      Tuesday
  ... ... ... ... ...
  222020  11-30   3:50:00   PM      Monday
  222021  11-30   3:55:00   PM      Monday
  222022  11-30   4:00:00   PM      Monday
  222023  11-30   4:05:00   PM      Monday
  222024  11-30   4:10:00   PM      Monday
  </code></pre>
  <p>They are <strong>not</strong> datetime objects however...</p>
  <pre><code>&lt;class 'pandas.core.frame.DataFrame'&gt;
  RangeIndex: 221945 entries, 80 to 222024
  Data columns (total 4 columns):
   #   Column    Non-Null Count   Dtype 
  ---  ------    --------------   ----- 
   0   Date      221945 non-null  object
   1   Time      221945 non-null  object
   2   Meridiem  221945 non-null  object
   3   Day       221945 non-null  object
  dtypes: object(4)
  </code></pre>
  <p>I need to add a column for 'Year' for this dataframe.
  The data is in order and each row is in interval of 5 minutes from 9:35AM to 4:15PM (business days only), starting from 2010-01-05 to 2020-11-30 (approx. 11 years).</p>
  <p>What would be the easiest way to add the year column? I suppose I can just manually locate the row index of last day of the year and add the year as it's only 11 items but I wanted to know if there is an easier way to do it?</p>