title: python dataframe sum function returning negative number
body: <p>I am working with a test dataset of the Lending Club loan data and am trying to create some analysis with the set.</p>
  
  <p>After loading the csv into a dataframe, I am just trying to do a simple sum on the entire funded_amnt column.  I keep receiving a negative amount for the sum even though there are no negative numbers in the entire set.  How can this be?</p>
  
  <pre><code>In[ ]: loans_df['funded_amnt'].sum()
  
  Out[ ]: -1925852142
  
  In[ ]: len(loans_df[loans_df['funded_amnt']&lt;0])
  
  Out[ ]: 0
  </code></pre>