how to add an item to OrderedDict

Question

I have an OrderedDict, I need to add an element while maintaining sorting

import sys
import bisect
from collections import OrderedDict

arr = {('a',1111),('b',2222),('f',3333)}
arr = OrderedDict(arr)

bisect.insort(arr,('c',4444))
#expectedly      arr = {('a',1111),('b',2222),('c',4444),('f',3333)}

#but actually     TypeError: collections.OrderedDict is not a sequence

Update: I need items to be stored sorted by key but with

import sys
import bisect
from collections import OrderedDict
from sortedcontainers import sorteddict
arr = {('a',1111),('b',2222),('f',3333)}
arr = OrderedDict(arr)
arr.update({'c':4444})   #or arr['c'] = 4444
print(arr)

OrderedDict([('b', 2222), ('f', 3333), ('a', 1111), ('c', 4444)])

instead OrderedDictх([('a',1111),('b',2222),('c',4444),('f',3333)])

like map in c ++

Answer 1

Add the new item to the original items, sort, make a new dict:

>>> arr = {('a',1111),('b',2222),('f',3333)}
>>> arr = collections.OrderedDict(arr)
>>> new = ('c',4444)
>>> items = list(arr.items())
>>> items.append(new)
>>> items.sort()
>>> arr = collections.OrderedDict(items)
>>> arr
OrderedDict([('a', 1111), ('b', 2222), ('c', 4444), ('f', 3333)])

---

Or a bit more involved option:

• Subclass collections.OrderedDict
• Using the move_to_end method as a guide create a new method that will traverse the doubly linked list; find the place to insert; then insert the new key - maybe bisect can be used here or some other doubly linked list sorted insertion algorithm
• override the __setitem__ method and within it call the new method - or just replace the add-new-key-to-the-end code with the algorithm you came up with in the previous bullet.

---

Sorted dict that maintains key sorted order

I couldn't figure out how to make an OrderedDict subclass work - it has a number of attributes that get name mangled - only one or two methods need to be overridden and I didn't want to spend the time figuring out the name-mangling aspect.

So just copy the whole OrderedDict class from the source from here - to here into a separate module, so you can import it, and include these imports.

from _weakref import proxy as _proxy
from collections import _Link, _OrderedDictKeysView
from collections import _OrderedDictItemsView, _OrderedDictValuesView
import _collections_abc
from _weakref import proxy as _proxy
from reprlib import recursive_repr as _recursive_repr
from operator import itemgetter as _itemgetter, eq as _eq
import bisect

Then change the following in the class:

• The class name of course to whatever you like. Following the class name is a docstring and some comments describing the class's behaviour - these should be updated.

    class SortOrderedDict(dict):

• Override the __setitem__ method. The following uses bisect to find the insertion order. Don't know if it is really warranted, it has to make a list of a dict keys view first but that part should be fast C code (? guessing here)

    def __setitem__(self, key, value,
                    dict_setitem=dict.__setitem__, proxy=_proxy, Link=_Link):
        'od.__setitem__(i, y) <==> od[i]=y'
        # Setting a new item creates a new link in the linked list,
        # inserted at its key sorted position - uses less than comparisons,
        # and the inherited dictionary is updated with the new key/value pair.
        if key not in self:
            self.__map[key] = link = Link()
            root = self.__root
            last = root.prev
            link.key = key
            curr = root.next
            if curr is root:    # first item!
                link.prev, link.next = last, root
                last.next = link
                root.prev = proxy(link)
            elif link.key < root.next.key:    # at the beginning?
                #print(f'{link.key} before {root.next.key}')
                soft_link = root.next
                link.prev, link.next = root, soft_link
                soft_link.prev = link
                root.next = link
            elif root.prev.key < link.key:    # at the end?
                #print(f'{link.key} at the end after {root.prev.key}')
                soft_link = root.prev
                link.prev, link.next = soft_link, root
                soft_link.next = link
                root.prev = proxy(link)
            else:    # in the middle somewhere - use bisect
                keys = list(self.keys())
                i = bisect.bisect_left(keys,key)
                right = self.__map[keys[i]]
                #print(f'{link.key} between {right.prev.key} and {right.key}')
                soft_link = right.prev
                link.prev,link.next = soft_link,right
                right.prev = link
                soft_link.next = link

        dict_setitem(self, key, value)

• Add an update method - this class is a subclass of dict this overrides its update method forcing it to use __setitem__.

    def update(self,other):
        try:
            other = other.items()
        except AttributeError:
            pass
        for k,v in other:
            self[k] = v

• Change this line update = __update = _collections_abc.MutableMapping.update to

    __update = update

• In the __reduce__ method change the class name in for k in vars(OrderedDict()): to whatever you you named your class

    for k in vars(SortOrderedDict()):

• Same thing in the __eq__ method. Change if isinstance(other, OrderedDict): to

    if isinstance(other, SortOrderedDict):

---

If using bisect doesn't seem worthwhile just traverse the linked list till the insertion point is found. (All the other changes listed above still apply)

    def __setitem__(self, key, value,
                    dict_setitem=dict.__setitem__, proxy=_proxy, Link=_Link):
        'od.__setitem__(i, y) <==> od[i]=y'
        # Setting a new item creates a new link in the linked list,
        # inserted at its key sorted position - uses less than comparisons,
        # and the inherited dictionary is updated with the new key/value pair.
        if key not in self:
            self.__map[key] = link = Link()
            root = self.__root
            last = root.prev
            link.key = key
            curr = root.next
            if curr is root:    # first item!
                link.prev, link.next = last, root
                last.next = link
                root.prev = proxy(link)
            # traverse the linked list; find sorted insertion point; insert
            while curr is not root:
                if link.key < curr.key:
                    soft_link = curr.prev
                    soft_link.next = link
                    link.prev = soft_link
                    link.next = curr
                    curr.prev = link
                    break
                elif curr.next is root:
                    link.prev, link.next = curr, root
                    curr.next = link
                    root.prev = proxy(link)
                    break
                curr = curr.next
        dict_setitem(self, key, value)

Usage

>>> arr = {('a',1111),('f',3333),('b',2222)}
>>> arr = SortOrderedDict(arr)
>>> arr
SortOrderedDict([('a', 1111), ('b', 2222), ('f', 3333)])
>>> other = {k:v for k,v in zip('tvsnpqkl',range(8))}
>>> arr.update(other)
>>> arr
SortOrderedDict([('a', 1111), ('b', 2222), ('f', 3333), ('k', 6), ('l', 7), ('n', 3), ('p', 4), ('q', 5), ('s', 2), ('t', 0), ('v', 1)])
>>> b = SortOrderedDict((('a',1111),('f',3333),('b',2222)))
>>> b.update(other)
>>> arr == b
True
>>> b == arr
True
>>>