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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clean(self):
 """Verifies that beginning date is before ending date."""

        cleaned_data = super(DatasetUploadForm, self).clean()
        date_begin = self.cleaned_data.get('date_begin')
        date_end = self.cleaned_data.get('date_end')
        if date_end < date_begin:
            msg = u'End date should be after start date.'
            self.add_error('date_begin', msg)
            self.add_error('date_end', msg)
        return cleaned_data