title: python string replacement with % character/**kwargs weirdness
body: <p>Following code:</p>
  
  <pre><code>def __init__(self, url, **kwargs):
      for key in kwargs.keys():
          url = url.replace('%%s%' % key, str(kwargs[key]))
  </code></pre>
  
  <p>Throws the following exception:</p>
  
  <pre><code>File "/home/wells/py-mlb/lib/fetcher.py", line 25, in __init__
  url = url.replace('%%s%' % key, str(kwargs[key]))
  ValueError: incomplete format
  </code></pre>
  
  <p>The string has a format like:</p>
  
  <pre><code>http://www.blah.com?id=%PLAYER_ID%
  </code></pre>
  
  <p>What am I doing wrong?</p>