title: Pandas to_csv(sys.stdout) doesn't work under my environment
body: <p>I ran a following simple script:</p>
  
  <pre><code>import sys
  import pandas as pd
  df = pd.DataFrame([[1,2,3], [4,5,6]])
  df.to_csv(sys.stdout)
  </code></pre>
  
  <h2>Expected Output (as standard output)</h2>
  
  <pre><code>,0,1,2
  0,1,2,3
  1,4,5,6
  </code></pre>
  
  <p>However, I got no outputs on standard output by the program under Python 2.7.15 on macOS 10.12.6. Instead, it generated a file named <code>&lt;stdout&gt;</code> which contains the expected output.</p>
  
  <p>Interestingly, on the same OS, Python 3.6.5 could show the result as standard output without any problems, and <em>virtualenved</em> Python 3.6.5 could not show it (and generated the <code>&lt;stdout&gt;</code> file).</p>
  
  <p>Does anyone identify the cause of this result? The version of Pandas is 0.23.1.</p>