code: def attribute(element, attribute, default=None):
      
      attribute_value = element.get(attribute)
  
      return attribute_value if attribute_value is not None else default
docs: Returns the value of an attribute, or a default if it's not defined
      :param element: The XML Element object
      :type  element: etree._Element
  
      :param attribute: The name of the attribute to evaluate
      :type  attribute: basestring
  
      :param default: The default value to return if the attribute is not defined