Python 3.5.1 扩展列表

Question

sorry to repost (I've just joined stack overflow 30 mins ago). I don't think I explained in my previous post of my function.

def GetExtendedKeyword(message, newkeyword):
    while True:
        difference = len(message) - len(newkeyword)
        if difference > 0:
            newkeyword.extend(newkeyword[:difference]
            return newkeyword
        elif difference <= 0:
            return newkeyword

What I have are two lists, a message and keyword list. The program calculates the difference between them and if the keyword is shorter than the message list, the program will repeat the keywordlist by that difference.

For example the original keywordlist is [0,1,5,2,5] and the difference is 3, the end result should be [0,1,5,2,5,0,1,5] . The program doesn't like my code when it comes to longer keyword or message lists. Please help!

Answer 1

Try it like this

l = [0, 1, 5, 4, 2, 9]
l.extend(l[:n]) #extend l with the first n elements of l

This only works for n < len(l) ...

Answer 2

If the amount can be larger than the list length, you can do this:

def extend(lst, n):
    nfull = n / len(lst) + 1
    nrem = n % len(lst)
    return lst*nfull+lst[:nrem]

lst = [0,1,5,4,2,9]
print extend(lst, 3)
# [0, 1, 5, 4, 2, 9, 0, 1, 5]
print extend(lst, 7)
# [0, 1, 5, 4, 2, 9, 0, 1, 5, 4, 2, 9, 0]

Answer 3

list.extend(L) Extend the list by appending all the items in the given list; equivalent to a[len(a):] = L.

It's sentence from Python Documentation. I think it is the best place where you should looking for a help. Acording to documentation, your code should look like this:

listOne = [0,1,5,4,2,9]
listOne.extend(listOne[:n])

I wonder to help you.