title: How colon(:) works in python & pandas?
body: <p>I create a DataFrame：</p>
  
  <pre><code>import pandas as pd
  data = pd.DataFrame({'a':range(1,11),'b':['m','f','m','m','m','f','m','f','f','f'],'c':np.random.randn(10)})
  </code></pre>
  
  <p>Which looks like：</p>
  
  <pre><code>    a  b         c
  0   1  m  0.495439
  1   2  f  1.444694
  2   3  m  0.150637
  3   4  m -1.078252
  4   5  m  0.618045
  5   6  f -0.525368
  6   7  m  0.188912
  7   8  f  0.159014
  8   9  f  0.536495
  9  10  f  0.874598
  </code></pre>
  
  <p>When I want to select some rows, I run</p>
  
  <pre><code>data[:2] or data.ix[2]
  </code></pre>
  
  <p>But when I try:</p>
  
  <pre><code>se = range(2)
  data[se]
  </code></pre>
  
  <p>There's a error:</p>
  
  <pre><code>KeyError: 'No column(s) named: [0 1]'
  </code></pre>
  
  <p>I know DataFrame select a col as default.What happened when I run <code>data[se]</code>?
  How colon(:) works in python?</p>