insert() 方法中的字典理解不起作用

Question

我正在制作一个 MappingList class，这是一个作为 OrderedDict.

实现的列表

这是MappingListclass（部分方法省略）：

class MappingList(MutableSequence):
    """
    A MappingList is a regular list implemented as a dictionary
    """

    def __repr__(self):
        return str(list(self.seq.values()))

    def __getitem__(self, item):
        try:
            return self.seq[item]
        except KeyError:
            _traceback_from_none(IndexError, "list index out of range")

    def __setitem__(self, key, value, *, usage=None):
        if key > max(self.seq.keys()) and usage != "append":
            raise IndexError("list index out of range")
        self.seq[key] = value

    def __delitem__(self, key):
        try:
            del self.seq[key]
        except KeyError:
            _traceback_from_none(IndexError, "list index out of range")

    def __len__(self):
        return len(self.seq)

    def __eq__(self, other):
        if not isinstance(other, MappingList):
            return NotImplemented
        return self.seq == other.seq

    @classmethod
    def _dict_from_seq(cls, seq):
        return OrderedDict(enumerate(seq))

    def _next_available_slot(self):
        return max(self.seq) + 1

    def insert(self, index, value):  # todo: insert() should not overwrite
        """Insert a value into the MappingList"""
        if index > max(self.seq.keys()):
            raise IndexError("list index out of range")

        for k, v in {k: v for k, v in self.seq.items() if k > index}:
            del self.seq[k]
            self.seq[k + 1] = v

        self[index] = value

当我尝试将项目插入 MappingList 时，出现以下错误：

  File "C:\...\My Python Programs\free_time\mappinglist.py", line 103, in test_insert
    self.li.insert(1, MappingList(["blah", 1, 5.8]))
  File "C:\...\My Python Programs\free_time\mappinglist.py", line 85, in insert
    for k, v in {k: v for k, v in self.seq.items() if k > index}:
TypeError: cannot unpack non-iterable int object

为什么会出现这个错误？ OrderedDict.items() return 是整数吗？

Answer 1

错误不会因此发生。

当您不提供 keys(), values(), items() 时，python 默认会遍历键。您需要提供 items() 来告诉 python 获取键和值。

for k, v in {k: v for k, v in self.seq.items() if k > index}.items():

insert() 方法中的字典理解不起作用

Dictionary comprehension inside insert() method not working

python

dictionary

python-3.x

dictionary-comprehension