title: Python enumeration/row counter in a pandas column
body: <p>Hello fellow stackoverflowers,</p>
  
  <p>New to the community with a Python (pandas/numpy) question.</p>
  
  <p>I'm using pandas and numpy to create a sample dataframe for testing.  However, for several reasons, I need one of the colums to be an enumerator, or row counter, if you will.  I've tried the enumerate function:</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  
  N = 100
  sample_data = pd.DataFrame({       
    'A': np.random.rand(N),
    'B': enumerate('A',1)})
  </code></pre>
  
  <p>but I keep getting this error:
      TypeError: object of type 'enumerate' has no len()</p>
  
  <p>How do I go about doing this in the most efficient way possible?</p>
  
  <p>Thanks!</p>