title: Print string left aligned with fixed width and suffix
body: <p>Using Pythons string formatting, is there a nice way to add a suffix to a left aligned string that is padded to a fixed size?</p>
  
  <p>I want to print a list of key-value-pairs in the following formatting:</p>
  
  <pre><code>a_key:        23
  another_key:  42
  ...
  </code></pre>
  
  <p>The problem is the ':'. The best solution I found so far is to append the ':' to the key name:</p>
  
  <pre><code>print "{:&lt;20}  {}".format(key+':', value)
  </code></pre>
  
  <p>But I think this is a rather ugly solution, as it diminishes the separation of formatting and values. Is it possible to achieve this directly in the format specification?</p>
  
  <p>What I am looking for is something like this:</p>
  
  <pre><code>print "{do something here}  {}".format(key, value)
  </code></pre>