# Copyright 2009-2024 Joshua Bronson. All rights reserved.
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
# * Code review nav *
# (see comments in __init__.py)
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# ← Prev: _bidict.py Current: _orderedbase.py Next: _orderedbidict.py →
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"""Provide :class:`OrderedBidictBase`."""
from __future__ import annotations
import typing as t
from weakref import ref as weakref
from ._base import BidictBase
from ._base import Unwrites
from ._bidict import bidict
from ._iter import iteritems
from ._typing import KT
from ._typing import MISSING
from ._typing import OKT
from ._typing import OVT
from ._typing import VT
from ._typing import MapOrItems
AT = t.TypeVar('AT') # attr type
class WeakAttr(t.Generic[AT]):
"""Descriptor to automatically manage (de)referencing the given slot as a weakref.
See https://docs.python.org/3/howto/descriptor.html#managed-attributes
for an intro to using descriptors like this for managed attributes.
"""
def __init__(self, *, slot: str) -> None:
self.slot = slot
def __set__(self, instance: t.Any, value: AT) -> None:
setattr(instance, self.slot, weakref(value))
def __get__(self, instance: t.Any, __owner: t.Any = None) -> AT:
return t.cast(AT, getattr(instance, self.slot)())
class Node:
"""A node in a circular doubly-linked list
used to encode the order of items in an ordered bidict.
A weak reference to the previous node is stored
to avoid creating strong reference cycles.
Referencing/dereferencing the weakref is handled automatically by :class:`WeakAttr`.
"""
prv: WeakAttr[Node] = WeakAttr(slot='_prv_weak')
__slots__ = ('__weakref__', '_prv_weak', 'nxt')
nxt: Node | WeakAttr[Node] # Allow subclasses to use a WeakAttr for nxt too (see SentinelNode)
def __init__(self, prv: Node, nxt: Node) -> None:
self.prv = prv
self.nxt = nxt
def unlink(self) -> None:
"""Remove self from in between prv and nxt.
Self's references to prv and nxt are retained so it can be relinked (see below).
"""
self.prv.nxt = self.nxt
self.nxt.prv = self.prv
def relink(self) -> None:
"""Restore self between prv and nxt after unlinking (see above)."""
self.prv.nxt = self.nxt.prv = self
class SentinelNode(Node):
"""Special node in a circular doubly-linked list
that links the first node with the last node.
When its next and previous references point back to itself
it represents an empty list.
"""
nxt: WeakAttr[Node] = WeakAttr(slot='_nxt_weak')
__slots__ = ('_nxt_weak',)
def __init__(self) -> None:
super().__init__(self, self)
def iternodes(self, *, reverse: bool = False) -> t.Iterator[Node]:
"""Iterator yielding nodes in the requested order."""
attr = 'prv' if reverse else 'nxt'
node = getattr(self, attr)
while node is not self:
yield node
node = getattr(node, attr)
def new_last_node(self) -> Node:
"""Create and return a new terminal node."""
old_last = self.prv
new_last = Node(old_last, self)
old_last.nxt = self.prv = new_last
return new_last
class OrderedBidictBase(BidictBase[KT, VT]):
"""Base class implementing an ordered :class:`BidirectionalMapping`."""
_node_by_korv: bidict[t.Any, Node]
_bykey: bool
[docs]
def __init__(self, arg: MapOrItems[KT, VT] = (), /, **kw: VT) -> None:
"""Make a new ordered bidirectional mapping.
The signature behaves like that of :class:`dict`.
Items passed in are added in the order they are passed,
respecting the :attr:`~bidict.BidictBase.on_dup`
class attribute in the process.
The order in which items are inserted is remembered,
similar to :class:`collections.OrderedDict`.
"""
self._sntl = SentinelNode()
self._node_by_korv = bidict()
self._bykey = True
super().__init__(arg, **kw)
if t.TYPE_CHECKING:
@property
def inverse(self) -> OrderedBidictBase[VT, KT]: ...
@property
def inv(self) -> OrderedBidictBase[VT, KT]: ...
def _make_inverse(self) -> OrderedBidictBase[VT, KT]:
inv = t.cast(OrderedBidictBase[VT, KT], super()._make_inverse())
inv._sntl = self._sntl
inv._node_by_korv = self._node_by_korv
inv._bykey = not self._bykey
return inv
def _assoc_node(self, node: Node, key: KT, val: VT) -> None:
korv = key if self._bykey else val
self._node_by_korv.forceput(korv, node)
def _dissoc_node(self, node: Node) -> None:
del self._node_by_korv.inverse[node]
node.unlink()
def _init_from(self, other: MapOrItems[KT, VT]) -> None:
"""See :meth:`BidictBase._init_from`."""
super()._init_from(other)
bykey = self._bykey
korv_by_node = self._node_by_korv.inverse
korv_by_node.clear()
korv_by_node_set = korv_by_node.__setitem__
self._sntl.nxt = self._sntl.prv = self._sntl
new_node = self._sntl.new_last_node
for k, v in iteritems(other):
korv_by_node_set(new_node(), k if bykey else v)
def _write(self, newkey: KT, newval: VT, oldkey: OKT[KT], oldval: OVT[VT], unwrites: Unwrites | None) -> None:
"""See :meth:`bidict.BidictBase._spec_write`."""
super()._write(newkey, newval, oldkey, oldval, unwrites)
assoc, dissoc = self._assoc_node, self._dissoc_node
node_by_korv, bykey = self._node_by_korv, self._bykey
if oldval is MISSING and oldkey is MISSING: # no key or value duplication
# {0: 1, 2: 3} | {4: 5} => {0: 1, 2: 3, 4: 5}
newnode = self._sntl.new_last_node()
assoc(newnode, newkey, newval)
if unwrites is not None:
unwrites.append((dissoc, newnode))
elif oldval is not MISSING and oldkey is not MISSING: # key and value duplication across two different items
# {0: 1, 2: 3} | {0: 3} => {0: 3}
# n1, n2 => n1 (collapse n1 and n2 into n1)
# oldkey: 2, oldval: 1, oldnode: n2, newkey: 0, newval: 3, newnode: n1
if bykey:
oldnode = node_by_korv[oldkey]
newnode = node_by_korv[newkey]
else:
oldnode = node_by_korv[newval]
newnode = node_by_korv[oldval]
dissoc(oldnode)
assoc(newnode, newkey, newval)
if unwrites is not None:
unwrites.extend((
(assoc, newnode, newkey, oldval),
(assoc, oldnode, oldkey, newval),
(oldnode.relink,),
))
elif oldval is not MISSING: # just key duplication
# {0: 1, 2: 3} | {2: 4} => {0: 1, 2: 4}
# oldkey: MISSING, oldval: 3, newkey: 2, newval: 4
node = node_by_korv[newkey if bykey else oldval]
assoc(node, newkey, newval)
if unwrites is not None:
unwrites.append((assoc, node, newkey, oldval))
else:
assert oldkey is not MISSING # just value duplication
# {0: 1, 2: 3} | {4: 3} => {0: 1, 4: 3}
# oldkey: 2, oldval: MISSING, newkey: 4, newval: 3
node = node_by_korv[oldkey if bykey else newval]
assoc(node, newkey, newval)
if unwrites is not None:
unwrites.append((assoc, node, oldkey, newval))
[docs]
def __iter__(self) -> t.Iterator[KT]:
"""Iterator over the contained keys in insertion order."""
return self._iter(reverse=False)
[docs]
def __reversed__(self) -> t.Iterator[KT]:
"""Iterator over the contained keys in reverse insertion order."""
return self._iter(reverse=True)
def _iter(self, *, reverse: bool = False) -> t.Iterator[KT]:
nodes = self._sntl.iternodes(reverse=reverse)
korv_by_node = self._node_by_korv.inverse
if self._bykey:
for node in nodes:
yield korv_by_node[node]
else:
key_by_val = self._invm
for node in nodes:
val = korv_by_node[node]
yield key_by_val[val]
# * Code review nav *
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