code: def clean(cls, cnpj):
          u
          if isinstance(cnpj, six.string_types):
              cnpj = int(re.sub('[^0-9]', '', cnpj))
  
          return '{0:014d}'.format(cnpj)
docs: u"""
          Retorna apenas os dígitos do CNPJ.
  
          >>> CNPJ.clean('58.414.462/0001-35')
          '58414462000135'