code: def get_files(cls, folder):
          
          filelist = []
          if folder is None or not os.path.isdir(folder):
              return filelist
          for root, dirs, files in os.walk(folder):
              for filename in files:
                  filename = os.path.join(root, filename)
                  if is_csv_file(filename):
                      filelist.append(filename)
          return filelist
docs: Retrieve the list of files the plugin can work on.
          Find this list based on the files name, files extension or even
          actually by reading in the file.
  
          :arg folder: the path to the folder containing the files to
              check. This folder may contain sub-folders.