无法在Python中反转列表，从而获取"Nonetype"作为清单 [英] Unable to reverse lists in Python, getting "Nonetype" as list

问题描述

我有一个.py文件，该文件带有一个列表，查找最低编号，将其放入新数组中，从第一个数组中删除最低编号，然后重复执行，直到原始数组返回不再包含更多项目为止:

I have a .py file that takes a list, finds the lowest number, puts it into a new array, removes the lowest number from the first array, and repeats until the original array returns contains no more items:

def qSort(lsort):
    listlength = len(lsort)
    sortedlist = list()
    if listlength == 0:
        return lsort
    else:
        while listlength > 0:
            lmin = min(lsort)
            sortedlist.append(lmin)
            lsort.remove(lmin)
            listlength = len(lsort)
        return sortedlist

现在，另一个.py文件将导入qSort并将其在某些列表上运行，并将其保存到变量中.然后，我尝试在列表上使用.reverse()命令，最终得到了NoneType的身份.我尝试使用reversed()，但所做的只是说"<listreverseiterator object at 0xSomeRandomHex>":

Now another .py file imports the qSort and runs it on some list, saving it to a variable. Then I try to use the .reverse() command on the list and I end up getting it as a NoneType. I try to use reversed(), but all it does is say "<listreverseiterator object at 0xSomeRandomHex>":

from qSort import qSort #refer to my first Pastebin

qSort = qSort([5,42,66,1,24,5234,62])
print qSort #this prints the sorted list
print type(qSort) #this prints <type 'list'>
print qSort.reverse() #this prints None
print reversed(qSort) #this prints "<listreverseiterator object at 0xSomeRandomHex>"

任何人都可以解释为什么不管我做什么我似乎都无法撤消名单吗?

Can anyone explain why I can't seem to reverse the list, no matter what I do?

推荐答案

正如jcomeau所提到的，.reverse()函数会在适当的位置更改列表.它不会返回列表，而是会更改qSort.

As jcomeau mentions, the .reverse() function changes the list in place. It does not return the list, but rather leaves qSort altered.

如果您要返回"已反转的列表，因此可以像在示例中尝试的那样使用它，则可以以-1的方向进行切片

If you want to 'return' the reversed list, so it can be used like you attempt in your example, you can do a slice with a direction of -1

因此将print qSort.reverse()替换为print qSort[::-1]

您应该了解切片及其有用的内容.我没有真正在本教程中看到一个同时描述所有地方的地方，( http ://docs.python.org/tutorial/introduction.html#lists 并未真正涵盖所有内容)，因此希望这里有一些说明性示例.

You should know slices, its useful stuff. I didn't really see a place in the tutorial where it was all described at once, (http://docs.python.org/tutorial/introduction.html#lists doesn't really cover everything) so hopefully here are some illustrative examples.

语法是:a[firstIndexInclusive:endIndexExclusive:Step]

>>> a = range(20)
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>> a[7:] #seventh term and forward
[7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>> a[:11] #everything before the 11th term
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[::2] # even indexed terms.  0th, 2nd, etc
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
>>> a[4:17]
[4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
>>> a[4:17:2]
[4, 6, 8, 10, 12, 14, 16]
>>> a[::-1]
[19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
>>> a[19:4:-5]
[19, 14, 9]
>>> a[1:4] = [100, 200, 300] #you can assign to slices too
>>> a
[0, 100, 200, 300, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

这篇关于无法在Python中反转列表，从而获取"Nonetype"作为清单的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！