code: def add_postfix(file_path, postfix):
          # type: (AnyStr, AnyStr) -> AnyStr
          
          cur_sep = ''
          for sep in ['\\', '/', os.sep]:
              if sep in file_path:
                  cur_sep = sep
                  break
          corename = FileClass.get_core_name_without_suffix(file_path)
          tmpspliter = os.path.basename(file_path).split('.')
          suffix = ''
          if len(tmpspliter) > 1:
              suffix = tmpspliter[-1]
          newname = os.path.dirname(file_path) + cur_sep + corename + '_' + postfix
          if suffix != '':
              newname += '.' + suffix
          return str(newname)
docs: Add postfix for a full file path.
  
          Examples:
              >>> FileClass.add_postfix('/home/zhulj/dem.tif', 'filled')
              '/home/zhulj/dem_filled.tif'
              >>> FileClass.add_postfix('dem.tif', 'filled')
              'dem_filled.tif'
              >>> FileClass.add_postfix('dem', 'filled')
              'dem_filled'