title: Python itertools combinations length
body: <p>Would appreciate any input about this practice problem:</p>
  
  <p>Given a string of length <code>n</code> and an integer <code>k</code>, print all possible combinations of length <code>k</code> (Print nCk) under the constraint that <code>1</code> &lt;= <code>k</code> &lt;= <code>n</code>. You can assume no repeating characters</p>
  
  <p>Examples:</p>
  
  <blockquote>
    <p>abc, 2 --> ab, bc, ca</p>
    
    <p>abc, 1 --> a, b, c</p>
    
    <p>abc, 3 --> abc</p>
  </blockquote>