title: scikit-learn convention for label-inputs in data set
body: <p>Is there any general format for label-inputs in scikit-learn datasets? I see it have list of labels for output in <code>target_names</code>. I want to follow scikit conventions and keep some data about labels in input vars (e.g. sex). Is there any convention for this allready? Something like this</p>
  
  <pre><code>&gt;&gt;&gt; data_set.inputs["sex"]
  {'male': 1, 'female': 0}
  </code></pre>