title: python sum a column's value with condition
body: <p>I have the below dataframe. I would like to return a second column that is the sum of every item in the column with a condition: only those larger than -1.</p>
  <p>input</p>
  <pre><code>   Price
  0    12
  1    14
  2    15
  3    10
  4     2
  5     4
  6    -5
  7    -4
  8    -3
  9    -5
  10   16
  11   15
  </code></pre>
  <p>output</p>
  <pre><code>   Price     Total Sum
  0    12          88
  1    14
  2    15
  3    10
  4     2
  5     4
  6    -5
  7    -4
  8    -3
  9    -5
  10   16
  11   15
  </code></pre>