def clean(self):
        if 'end' in self.cleaned_data and 'start' in self.cleaned_data:
            if self.cleaned_data['end'] <= self.cleaned_data['start']:
                raise forms.ValidationError(_(u"The end time must be later than start time."))
        return self.cleaned_data
dataset/ETHPy150Open llazzaro/django-scheduler/schedule/forms.py/SpanForm.clean/original