title: How is str.split implemented for a case without arguments
body: <p>Does Python use regex splitting when no separator is given? </p>
  
  <p>I'm unable to look at <code>str.__file__</code>, neither do the <a href="https://stackoverflow.com/questions/8608587/finding-the-source-code-for-built-in-python-functions">other solutions work</a> here since <code>split</code> is a function of the <code>str</code> type (though it is a built-in). </p>
  
  <p>E.g. <code>'a\t\t\tb' --&gt; ['a', 'b']</code></p>
  
  <p><strong>Background</strong> 
  I'm considering replacing all adjacent whitespace with a single space for many files where performance is critical, though I'm wondering whether regex split is going to be fast enough: perhaps the built-in shows a better way.</p>