title: Sum all columns in a Pandas DataFrame where there are non-numeric values
body: <p>I have the following dataset:</p>
  
  <pre><code>df = pd.DataFrame({'col1' : [12,3,4,5,'a',5], 'col2' : [1,5,'b',6,10,1]})
  </code></pre>
  
  <p>If I run <code>df.sum(axis=0, numeric_only=True)</code>, I get the following output:</p>
  
  <pre><code>Series([], dtype: float64)
  </code></pre>
  
  <p>However, if I change the non-numeric values to <code>None</code> then it works fine.</p>
  
  <p>So, my question is how can I find the sums of all the columns in my dataset when there are non-numeric values present?</p>