title: Better way to add constant column to pandas data frame
body: <p>Currently when I have to add a constant column to an existing data frame, I do the following. To me it seems not all that elegant (the part where I multiply by length of dataframe). Wondering if there are better ways of doing this. </p>
  
  <pre><code>import pandas as pd
  
  testdf = pd.DataFrame({'categories': ['bats', 'balls', 'paddles'],
                         'skus': [50, 5000, 32],
                         'sales': [500, 700, 90]})
  
  testdf['avg_sales_per_sku'] = [testdf.sales.sum() / testdf.skus.sum()] * len(testdf)
  </code></pre>