title: Appending rows to empty DataFrame not working
body: <p>I have a piece of Python code that essentially reduces to the following:</p>
  
  <pre><code>import pandas as pd
  
  months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
  l = [1607.8, 1688.17, 1605.66, 1469.03, 1312.65, 1451.74, 1445.26, 1350.94, 1371.27, 1201.6, 1240.59, 1291.43]
  
  # First, construct a empty DataFrame.
  df = pd.DataFrame(columns = months, dtype=float)
  
  # Then, keep adding rows to DataFrame given by list l.
  df.append([l])
  
  print df
  </code></pre>
  
  <p>Expected output is:</p>
  
  <pre><code>      Jan      Feb      Mar      Apr      May      Jun      Jul      Aug  \
  0  1607.8  1688.17  1605.66  1469.03  1312.65  1451.74  1445.26  1350.94   
  
         Sep     Oct      Nov      Dec  
  0  1371.27  1201.6  1240.59  1291.43  
  </code></pre>
  
  <p>However what I get is the following:</p>
  
  <pre><code>Empty DataFrame
  Columns: [Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec]
  Index: []
  </code></pre>
  
  <p>If I replace <code>df.append([l])</code> with the following, things work fine for me.</p>
  
  <pre><code>df = pd.DataFrame([l], columns = months)
  df.columns = months
  </code></pre>
  
  <p>What am I doing wrong?</p>