# From: https://github.com/ActiveState/code/blob/master/recipes/Python/576696_OrderedSet_with_Weakrefs/ # noqa
import typing as t
import weakref
class Link:
"""Representation of one item in a doubly-linked list."""
__slots__ = ("prev", "next", "key", "__weakref__")
prev: "Link"
next: "Link"
key: str
class OrderedSet(t.MutableSet[str]):
"""A set that remembers the order in which items were added."""
# Big-O running times for all methods are the same as for regular sets.
# The internal self.__map dictionary maps keys to links in a doubly linked
# list. The circular doubly linked list starts and ends with a sentinel
# element. The sentinel element never gets deleted (this simplifies the
# algorithm). The prev/next links are weakref proxies (to prevent circular
# references). Individual links are kept alive by the hard reference in
# self.__map. Those hard references disappear when a key is deleted from
# an OrderedSet.
def __init__(self, iterable: t.Optional[t.Iterable[str]] = None):
self.__root = root = Link() # sentinel node for doubly linked list
root.prev = root.next = root
self.__map: t.MutableMapping[str, Link] = {} # key --> link
if iterable is not None:
self |= iterable # type: ignore
def __len__(self) -> int:
return len(self.__map)
def __contains__(self, key: object) -> bool:
return key in self.__map
def add(self, key: str) -> None:
# Store new key in a new link at the end of the linked list
if key not in self.__map:
self.__map[key] = link = Link()
root = self.__root
last = root.prev
link.prev, link.next, link.key = last, root, key
last.next = root.prev = weakref.proxy(link)
def discard(self, key: str) -> None:
# Remove an existing item using self.__map to find the link which is
# then removed by updating the links in the predecessor and successors.
if key in self.__map:
link = self.__map.pop(key)
link.prev.next = link.next
link.next.prev = link.prev
def __iter__(self) -> t.Generator[str, None, None]:
# Traverse the linked list in order.
root = self.__root
curr = root.next
while curr is not root:
yield curr.key
curr = curr.next
def __reversed__(self) -> t.Generator[str, None, None]:
# Traverse the linked list in reverse order.
root = self.__root
curr = root.prev
while curr is not root:
yield curr.key
curr = curr.prev
def pop(self, last: bool = True) -> str:
if not self:
raise KeyError("set is empty")
key = next(reversed(self)) if last else next(iter(self))
self.discard(key)
return key
def __repr__(self) -> str:
if not self:
return f"{self.__class__.__name__}()"
return f"{self.__class__.__name__}({list(self)!r})"
def __str__(self) -> str:
return self.__repr__()
def __eq__(self, other: object) -> bool:
if isinstance(other, OrderedSet):
return len(self) == len(other) and list(self) == list(other)
other = t.cast(t.Iterable[str], other)
return not self.isdisjoint(other)
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