title: django overwrite form clean method
body: <p>When overwriting a form clean method how do you know if its failed validation on any of the fields? e.g.  in the form below if I overwrite the clean method how do I know if the form has failed validation on any of the fields?</p>
  
  <pre><code>class PersonForm(forms.Form):
      title = Forms.CharField(max_length=100)
      first_name = Forms.CharField(max_length=100)
      surname = Forms.CharField(max_length=100)
      password = Forms.CharField(max_length=100)
  
  def clean(self, value):
      cleaned_data = self.cleaned_data
  
      IF THE FORM HAS FAILED VALIDATION:
          self.data['password'] = 'abc'
          raise forms.ValidationError("You have failed validation!")
      ELSE:
          return cleaned_data 
  </code></pre>
  
  <p>Thanks</p>