如何在Python中提高for循环的效率

Question

I have a Python Code that produces all possible permutations of the words of a given sentence. And I want this permutations to be written in a .txt-document. If I try the code with a 9-word-long sentence, everything works fine. It takes a while but the file with all the possible permutations is created. But when I try the code with a 10-word-long sentence, it takes much to long because the possible permutations then are 10!. Is there a more efficient way to save all the permutations of a sentence in txt-file? I think the main problem is my for-loop.

parser = optparse.OptionParser(usage=help_text)
parser.add_option("-f", "--file", dest="filename",
                  help="write the permutations to FILE", metavar="FILE")
(options, args) = parser.parse_args()

# read the input
sentence = input("Sentence: ")
sent_list = re.split(r"[\s.,!?:\"\';()]+", sentence)
# remove empty strings from the sent_list
sent_list = [s for s in sent_list if s is not ""]

result = ""
perm_iterator = itertools.permutations(list(sent_list),r=None)


for item in perm_iterator:
    print("item in perm_iterator",item)
    result += "".join(item);



# print to file if file option is not None
if options.filename is not None:
    with open(options.filename, 'w') as f:
        f.write(result)
    print("The different variants of the sentence got saved in {} .".format(options.filename))
else:
    print(result)

Answer 1

The answer is no . The time complexity of such an operation will always be of the order of N!, since there are that many possilbe permutations. Reducing this asymptotically is mathematically impossible.