class MyUserAdminForm(forms.ModelForm):
    class Meta:
        model = User

    def __init__(self, *args, **kwargs):
        super(MyUserAdminForm, self).__init__(*args, **kwargs)
        instance = getattr(self, 'instance', None)
        if instance and instance.id: # username and user id
            self.fields['username'].widget.attrs['class'] = 'disabled'
            self.fields['username'].widget.attrs['readonly'] = True
            self.fields['is_superuser'].widget.attrs['class'] = 'disabled'
            self.fields['is_superuser'].widget.attrs['readonly'] = True
            new_text = '. <br \><span style="color: red;">Read-only field.\
                 To modify, do this via shell.</span>'
            self.fields['username'].help_text += new_text
            self.fields['is_superuser'].help_text += new_text

            if instance.is_superuser is True:
                self.fields['is_active'].widget.attrs['class'] = 'disabled'
                self.fields['is_active'].widget.attrs['readonly'] = 'readonly'
                new_text = '. <br \><span style="color: red;">This option\
                     is disabled for superuser. Do it via shell.</span>'
                self.fields['is_active'].help_text += new_text

    def clean_username(self):
        return self.instance.username

    def clean_is_superuser(self):
        return self.instance.is_superuser

    def clean_is_active(self):
        if self.instance.is_superuser is True:
            return self.instance.is_active
        else:
            return self.cleaned_data

    def save(self, *args, **kwargs):
        kwargs['commit'] = True
        user = super(MyUserAdminForm, self).save(*args, **kwargs)
        print user.username
        print 'done'
        return user