title: Python pylint(raising-format-tuple) Exception arguments suggest string formatting might be intended
body: <p>With a simple custom exception class defined as:</p>
  <pre><code>class MyError(Exception):
      pass
  </code></pre>
  <p>And this call:</p>
  <pre><code>foo = 'Some more info'
  raise MyError(&quot;%s: there was an error&quot;, foo)
  </code></pre>
  <p><code>pylint</code> gives:</p>
  <blockquote>
  <p>Exception arguments suggest string formatting might be intended <code>pylint(raising-format-tuple)</code></p>
  </blockquote>
  <p>What does this message mean?</p>