title: How to reference the empty string key in the Format String Syntax?
body: <p>The empty string (<code>''</code>) is a pertectly valid key for a dictionary, but I can not reference it using the <a href="https://docs.python.org/2/library/string.html#format-string-syntax" rel="noreferrer">Format String Syntax</a></p>
  
  <pre><code>data = { 'a' : 'hello' , '' : 'bye' }
  print '{a:&lt;14s}'.format(**data)
  print '{:&lt;14s}'.format(**data)
  </code></pre>
  
  <p>Which outputs:</p>
  
  <pre><code>hello         
  Traceback (most recent call last):
    File "xxx.py", line 3, in &lt;module&gt;
      print '{:&lt;14s}'.format(**data)
  IndexError: tuple index out of range
  </code></pre>
  
  <p>Is there any way of referencing that key ... as a dictionary key! I can not convert the data to tuples; a bit of background: I am doing some auto-formatting based on a generic format spec which gets converted to <code>Format String Syntax</code> using dicts as data for the formatting. That is, I can not do this:</p>
  
  <pre><code>print '{0:&lt;14s}'.format(data[''])
  </code></pre>
  
  <p>The data must always be passed to format as <code>**data</code> (basically, because I am doing a generic <code>.format(**data)</code> in my formatter class)</p>