I have a homogeneous list of objects with None, but it can contain any type of values. Example:
>>> 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]
Is there a way without reinventing the wheel to get the list sorted the usual python way, but with None values at the end of the list, like that:
[1, 2, 3, 4, 5, 7, None]
I feel like here can be some trick with "key" parameter
>>> l = [1, 3, 2, 5, 4, None, 7]
>>> sorted(l, key=lambda x: (x is None, x))
[1, 2, 3, 4, 5, 7, None]
这将为列表中的每个元素构造一个元组，如果值是None带有 be 的元组(True, None)，如果值是其他任何值(False, x)（值在哪里x）。由于元组是逐项排序的，这意味着所有非None元素将首先出现（从 开始False < True），然后按值排序。
尝试这个：
sorted(l, key=lambda x: float('inf') if x is None else x)
由于无穷大大于所有整数，所以None总是放在最后。
我创建了一个函数，扩展了 Andrew Clark 的答案和 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)
这是一个如何运行它的示例：
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))