title: Keyerror in multiple key string interpolation in Python
body: <p>I am having a problem like</p>
  
  <pre><code>In [5]: x = "this string takes two like {one} and {two}"
  
  In [6]: y = x.format(one="one")
  ---------------------------------------------------------------------------
  KeyError                                  Traceback (most recent call last)
  &lt;ipython-input-6-b3c89fbea4d3&gt; in &lt;module&gt;()
  ----&gt; 1 y = x.format(one="one")
  
  KeyError: 'two'
  </code></pre>
  
  <p>I have a compound string with many keys that gets kept in a config file. For 8 different queries, they all use the same string, except 1 key is a different setting. I need to be able to substitute a key in that file to save the strings for later like:</p>
  
  <pre><code>"this string takes two like one and {two}"
  </code></pre>
  
  <p>How do I substitute one key at a time using <code>format</code>? </p>