code: def check_files_exist(filenames):
      '''Dies if any files in the list of filenames does not exist'''
      files_not_found = [x for x in filenames if not os.path.exists(x)]
      if len(files_not_found):
          for filename in files_not_found:
              print('File not found: "', filename, '"', sep='', file=sys.stderr)
          raise Error('File(s) not found. Cannot continue'f check_files_exist(filenames):
      '''Dies if any files in the list of filenames does not exist'''
      files_not_found = [x for x in filenames if not os.path.exists(x)]
      if len(files_not_found):
          for filename in files_not_found:
              print('File not found: "', filename, '"', sep='', file=sys.stderr)
          raise Error('File(s) not found. Cannot continue')
docs: Dies if any files in the list of filenames does not exist