函数意外返回None

Question

Ok. So I finished this piece of code I have been working on, but I have a major problem. I doesn't return correctly.

if is_word(wordlist, decodedText):
        print 'entered if statement'
        print answer
        return answer

this is the piece of code that isn't working. The rest of the program isn't necessary. The line about entering the if statement was just a debug, so I would actually know that it did enter. The next print statement was to make sure that my variable answer actually was assigned to something, like it was elsewhere in the program. Now, this is what the code is giving me:

entered if statement [(0, -6), (3, -18), (12, -16)] None

I also tried using type(answer) to make sure that I didn't have some weird bug I wasn't seeing, but it was just saying it was a list.

So, why am I getting a None return??

answer = []
def find_best_shifts_rec(wordlist, text, start):
    """
    Given a scrambled string and a starting position from which
    to decode, returns a shift key that will decode the text to
    words in wordlist, or None if there is no such key.

    Hint: You will find this function much easier to implement
    if you use recursion.

    wordlist: list of words
    text: scambled text to try to find the words for
    start: where to start looking at shifts
    returns: list of tuples.  each tuple is (position in text, amount of shift)
    """
    global answer
    for shift in range(27):
        decodedText = apply_shift(text[start:], -shift)
        if is_word(wordlist, decodedText):
            print 'entered if statement'
            print answer
            return(answer)
        split = decodedText.split()
        if is_word(wordlist,split[0]) == True:
            answer.append((start, -shift))
            find_best_shifts_rec(wordlist, decodedText, (start+(len(split[0])+1)))
            break

print find_best_shifts_rec(wordlist, "JufYkaolfapxQdrnzmasmRyrpfdvpmEurrb?", 0)

This is the rest of my function. Let me know if there is something else you need to see.

Answer 1

the problem was you were not returning your recursive result ....

if is_word(wordlist,split[0]) == True:
        answer.append((start, -shift))
        return find_best_shifts_rec(wordlist, decodedText, (start+(len(split[0])+1)))