import os
import re
 
 
def auto_save_file(path):
  directory, file_name = os.path.split(path)
  while os.path.isfile(path):
    pattern = '(\d+)\)\.'
    if re.search(pattern, file_name) is None:
      file_name = file_name.replace('.', '(0).')
    else:
      current_number = int(re.findall(pattern, file_name)[-1])
      new_number = current_number + 1
      file_name = file_name.replace(f'({current_number}).', f'({new_number}).')
    path = os.path.join(directory + os.sep + file_name)
  return path

path = r'D:\test.txt'
for i in range(10):
  with open(auto_save_file(path), 'w') as f:
    f.write('This is a test!')