code: def get_name(cls, value):
          
          for member in cls:
              if member.value == value:
                  return member.name
          return str()
docs: Returns the `name` of the `Category` member with the matching *value*
          or a empty string if no member match.
  
          Example:
  
          >>> class Format(Category):
          ...     hour = 'hh'
          ...     minute = 'mm'
          ...     second = 'ss'
          >>> Format.get_name('hh')
          'hour'
          >>> Format.get_name('dd')
          ''