Question

我有具有None的同类对象列表，但它可以包含任何类型的值。例如：

>>> l = [1, 3, 2, 5, 4, None, 7]
>>> sorted(l)
[None, 1, 2, 3, 4, 5, 7]
>>> sorted(l, reverse=True)
[7, 5, 4, 3, 2, 1, None]

是否有办法在不重新发明轮子的情况下获取通常用于python方式的列表，但是在列表的末尾没有值，如：

[1, 2, 3, 4, 5, 7, None]

我觉得这里可以使用“key”参数

Answer 1

>>> l = [1, 3, 2, 5, 4, None, 7]
>>> sorted(l, key=lambda x: (x is None, x))
[1, 2, 3, 4, 5, 7, None]

这为列表中的每个元素构造一个元组，如果值为None，则元组为(True, None)，如果值为其他任何值，则为(False, x)（其中{ {1}}是值）。由于元组是逐项排序的，这意味着所有非x元素将首先出现（从None开始），然后按值排序。

Answer 2

试试这个：

sorted(l, key=lambda x: float('inf') if x is None else x)

由于无穷大大于所有整数，None将始终放在最后。

Answer 3

我创建了一个功能，扩展了Andrew Clark和tutuDajuju的评论。

def sort(myList, reverse = False, sortNone = False):
    """Sorts a list that may or may not contain None.
    Special thanks to Andrew Clark and tutuDajuju for how to sort None on https://stackoverflow.com/questions/18411560/python-sort-list-with-none-at-the-end

    reverse (bool) - Determines if the list is sorted in ascending or descending order

    sortNone (bool) - Determines how None is sorted
        - If True: Will place None at the beginning of the list
        - If False: Will place None at the end of the list
        - If None: Will remove all instances of None from the list

    Example Input: sort([1, 3, 2, 5, 4, None, 7])
    Example Input: sort([1, 3, 2, 5, 4, None, 7], reverse = True)
    Example Input: sort([1, 3, 2, 5, 4, None, 7], reverse = True, sortNone = True)
    Example Input: sort([1, 3, 2, 5, 4, None, 7], sortNone = None)
    """

    return sorted(filter(lambda item: True if (sortNone != None) else (item != None), myList), 
        key = lambda item: (((item is None)     if (reverse) else (item is not None)) if (sortNone) else
                            ((item is not None) if (reverse) else (item is None)), item), 
        reverse = reverse)

以下是如何运行它的示例：

myList = [1, 3, 2, 5, 4, None, 7]
print(sort(myList))
print(sort(myList, reverse = True))
print(sort(myList, sortNone = True))
print(sort(myList, reverse = True, sortNone = True))
print(sort(myList, sortNone = None))
print(sort(myList, reverse = True, sortNone = None))

Python排序列表最后为None

3 个答案: