title: Pandas - pct_change()
body: <p>I have downloaded some financial data from Yahoo finance and loaded in Python using Pandas. Now I am trying to use pct_change() but it's giving me an error</p>
  
  <p>Code used</p>
  
  <pre><code>sp = pd.read_csv('SP500.csv')
  sp=sp.set_index('Date')
  print(sp.head())
  ret=sp.pct_change()
  </code></pre>
  
  <p>Data Frame Head</p>
  
  <pre><code>             Open   High    Low  Close Adj Close   Volume
  Date                                                     
  03-01-1950  16.66  16.66  16.66  16.66     16.66  1260000
  04-01-1950  16.85  16.85  16.85  16.85     16.85  1890000
  05-01-1950  16.93  16.93  16.93  16.93     16.93  2550000
  06-01-1950  16.98  16.98  16.98  16.98     16.98  2010000
  09-01-1950  17.09  17.09  17.08  17.08     17.08  3850000
  </code></pre>
  
  <p>Error after pct_change()</p>
  
  <pre><code>TypeError: unsupported operand type(s) for /: 'str' and 'str'
  </code></pre>
  
  <p>Few top lines of the CSV file</p>
  
  <pre><code>Date,Open,High,Low,Close,Adj Close,Volume
  03-01-1950,16.66,16.66,16.66,16.66,16.66,1260000
  04-01-1950,16.85,16.85,16.85,16.85,16.85,1890000
  05-01-1950,16.93,16.93,16.93,16.93,16.93,2550000
  06-01-1950,16.98,16.98,16.98,16.98,16.98,2010000
  09-01-1950,17.09,17.09,17.08,17.08,17.08,3850000
  10-01-1950,17.030001,17.030001,17.030001,17.030001,17.030001,2160000
  11-01-1950,17.09,17.09,17.09,17.09,17.09,2630000
  12-01-1950,16.76,16.76,16.76,16.76,16.76,2970000
  13-01-1950,16.67,16.67,16.67,16.67,16.67,3330000
  16-01-1950,16.65,16.719999,16.65,16.719999,16.719999,2640000
  17-01-1950,16.860001,16.860001,16.860001,16.860001,16.860001,1790000
  18-01-1950,16.85,16.85,16.85,16.85,16.85,1570000
  19-01-1950,16.870001,16.870001,16.870001,16.870001,16.870001,1170000
  20-01-1950,16.9,16.9,16.9,16.9,16.9,1440000
  </code></pre>