title: How to select specific rows in a dataframe, group them and find the sum using python?
body: <p>Here is some example data:</p>
  <pre class="lang-py prettyprint-override"><code>mydf = {'Month': [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12],
          'Freq': [5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60]
          }
  my_df = pd.DataFrame(mydf, columns=['Month', 'Freq'])
  my_df
  
    Month Freq
  0   1   5
  1   2   10
  2   3   15
  3   4   20
  4   5   25
  5   6   30
  6   7   35
  7   8   40
  8   9   45
  9   10  50
  10  11  55
  11  12  60
  </code></pre>
  <p>How can I create a new dataframe which groups the months into seasons and find the total sum of each season frequency, while the output is still a dataframe?</p>
  <p>I would like something like this: (Winter is where Month = 12, 1, 2)(Spring is where Month = 3, 4, 5)(etc....)</p>
  <pre class="lang-py prettyprint-override"><code>   Season Freq
  0  Winter 75
  1  Spring 60
  2  Summer 105
  3  Autumn 150
  </code></pre>
  <p>I have tried to select the rows and concatenate them to start with but I keep getting errors unfortunately.</p>