Why django go on to clean datetime or date field?

问题:

when i use debugger, it does not go on this method, why ?

 def clean_duedate(self):
        import datetime
        date = self.cleaned_data['due_date']

        try:
            date = datetime.datetime.strftime(date, '%m/%d/%Y')
        except Exception as error:
           print(error)
           raise ValidationError('not date')
        return date