title: self.instance in Django ModelForm
body: <p>What does self.instance in Django ModelForm constructor mean and where can I find a documentation about it?</p>
  
  <pre><code>class MyModelForm(ModelForm):
      def __init__(self, *args, **kwargs):
          super(MyModelForm, self).__init__(*args, **kwargs)
          if self.instance:
          ...
  </code></pre>