'Make sure end date is greater than start date, when specified'

def clean_end(self):

    try:
        start = self.cleaned_data['start']
        if start:
            end = self.cleaned_data['end']
            if (end < start):
                raise forms.ValidationError(_('End    date    can    not    be    before    the    start    date'))
    except:
        pass
    return self.cleaned_data['end']
