在python中旋转列表最有效的方法是什么? 现在我有这样的东西:

>>> def rotate(l, n):
...     return l[n:] + l[:n]
... 
>>> l = [1,2,3,4]
>>> rotate(l,1)
[2, 3, 4, 1]
>>> rotate(l,2)
[3, 4, 1, 2]
>>> rotate(l,0)
[1, 2, 3, 4]
>>> rotate(l,-1)
[4, 1, 2, 3]

有没有更好的办法?


当前回答

我也有类似的事情。例如,移动两个…

def Shift(*args):
    return args[len(args)-2:]+args[:len(args)-2]

其他回答

以下函数将发送的列表复制到templist,这样pop函数不会影响原始列表:

def shift(lst, n, toreverse=False):
    templist = []
    for i in lst: templist.append(i)
    if toreverse:
        for i in range(n):  templist = [templist.pop()]+templist
    else:
        for i in range(n):  templist = templist+[templist.pop(0)]
    return templist

测试:

lst = [1,2,3,4,5]
print("lst=", lst)
print("shift by 1:", shift(lst,1))
print("lst=", lst)
print("shift by 7:", shift(lst,7))
print("lst=", lst)
print("shift by 1 reverse:", shift(lst,1, True))
print("lst=", lst)
print("shift by 7 reverse:", shift(lst,7, True))
print("lst=", lst)

输出:

lst= [1, 2, 3, 4, 5]
shift by 1: [2, 3, 4, 5, 1]
lst= [1, 2, 3, 4, 5]
shift by 7: [3, 4, 5, 1, 2]
lst= [1, 2, 3, 4, 5]
shift by 1 reverse: [5, 1, 2, 3, 4]
lst= [1, 2, 3, 4, 5]
shift by 7 reverse: [4, 5, 1, 2, 3]
lst= [1, 2, 3, 4, 5]

这取决于你这样做的时候想要发生什么:

>>> shift([1,2,3], 14)

你可能想要改变你的:

def shift(seq, n):
    return seq[n:]+seq[:n]

to:

def shift(seq, n):
    n = n % len(seq)
    return seq[n:] + seq[:n]

我认为你有最有效的方法

def shift(l,n):
    n = n % len(l)  
    return l[-U:] + l[:-U]

deque对两端的拉和推进行了优化。它们甚至有一个专用的rotate()方法。

from collections import deque
items = deque([1, 2])
items.append(3)        # deque == [1, 2, 3]
items.rotate(1)        # The deque is now: [3, 1, 2]
items.rotate(-1)       # Returns deque to original state: [1, 2, 3]
item = items.popleft() # deque == [2, 3]

对于一个不可变的实现,你可以使用这样的东西:

def shift(seq, n):
    shifted_seq = []
    for i in range(len(seq)):
        shifted_seq.append(seq[(i-n) % len(seq)])
    return shifted_seq

print shift([1, 2, 3, 4], 1)