title: add column to a dataframe in python pandas
body: <p>How do i loop through my excel sheet and add each 'Adjusted Close' to a dataframe? I want to summarize all adj close and make an stock indice.</p>
  
  <p>When i try with the below code the dataframe Percent_Change is empty.</p>
  
  <pre><code>xls = pd.ExcelFile('databas.xlsx')
  countSheets = len(xls.sheet_names)
  
  Percent_Change = pd.DataFrame()
  
  x = 0
  for x in range(countSheets):
      data = pd.read_excel('databas.xlsx', sheet_name=x, index_col='Date')
  
      # Calculate the percent change from day to day
      Percent_Change[x] = pd.Series(data['Adj Close'].pct_change()*100,     index=Percent_Change.index)
  
  
   stock_index = data['Percent_Change'].cumsum()
  </code></pre>