# -*- coding: utf-8 -*-
# Copyright 2009-2020 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/.
#==============================================================================
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"""Provides :class:`BidictBase`."""
from collections import namedtuple
from collections.abc import Mapping
from copy import copy
from weakref import ref
from ._abc import BidirectionalMapping
from ._dup import ON_DUP_DEFAULT, RAISE, DROP_OLD, DROP_NEW
from ._exc import (
DuplicationError, KeyDuplicationError, ValueDuplicationError, KeyAndValueDuplicationError)
from ._sntl import _MISS, _NOOP
from ._util import _iteritems_args_kw
_DedupResult = namedtuple('_DedupResult', 'isdupkey isdupval invbyval fwdbykey')
_WriteResult = namedtuple('_WriteResult', 'key val oldkey oldval')
_NODUP = _DedupResult(False, False, _MISS, _MISS)
[docs]class BidictBase(BidirectionalMapping):
"""Base class implementing :class:`BidirectionalMapping`."""
__slots__ = ('_fwdm', '_invm', '_inv', '_invweak', '_hash', '__weakref__')
#: The default :class:`~bidict.OnDup`
#: that governs behavior when a provided item
#: duplicates the key or value of other item(s).
#:
#: *See also* :ref:`basic-usage:Values Must Be Unique`, :doc:`extending`
on_dup = ON_DUP_DEFAULT
_fwdm_cls = dict
_invm_cls = dict
#: The object used by :meth:`__repr__` for printing the contained items.
_repr_delegate = dict
[docs] def __init__(self, *args, **kw): # pylint: disable=super-init-not-called
"""Make a new bidirectional dictionary.
The signature behaves like that of :class:`dict`.
Items passed in are added in the order they are passed,
respecting the :attr:`on_dup` class attribute in the process.
"""
#: The backing :class:`~collections.abc.Mapping`
#: storing the forward mapping data (*key* → *value*).
self._fwdm = self._fwdm_cls()
#: The backing :class:`~collections.abc.Mapping`
#: storing the inverse mapping data (*value* → *key*).
self._invm = self._invm_cls()
self._init_inv() # lgtm [py/init-calls-subclass]
if args or kw:
self._update(True, self.on_dup, *args, **kw)
def _init_inv(self):
# Compute the type for this bidict's inverse bidict (will be different from this
# bidict's type if _fwdm_cls and _invm_cls are different).
inv_cls = self._inv_cls()
# Create the inverse bidict instance via __new__, bypassing its __init__ so that its
# _fwdm and _invm can be assigned to this bidict's _invm and _fwdm. Store it in self._inv,
# which holds a strong reference to a bidict's inverse, if one is available.
self._inv = inv = inv_cls.__new__(inv_cls)
inv._fwdm = self._invm # pylint: disable=protected-access
inv._invm = self._fwdm # pylint: disable=protected-access
# Only give the inverse a weak reference to this bidict to avoid creating a reference cycle,
# stored in the _invweak attribute. See also the docs in
# :ref:`addendum:Bidict Avoids Reference Cycles`
inv._inv = None # pylint: disable=protected-access
inv._invweak = ref(self) # pylint: disable=protected-access
# Since this bidict has a strong reference to its inverse already, set its _invweak to None.
self._invweak = None
@classmethod
def _inv_cls(cls):
"""The inverse of this bidict type, i.e. one with *_fwdm_cls* and *_invm_cls* swapped."""
if cls._fwdm_cls is cls._invm_cls:
return cls
if not getattr(cls, '_inv_cls_', None):
class _Inv(cls):
_fwdm_cls = cls._invm_cls
_invm_cls = cls._fwdm_cls
_inv_cls_ = cls
_Inv.__name__ = cls.__name__ + 'Inv'
cls._inv_cls_ = _Inv
return cls._inv_cls_
@property
def _isinv(self):
return self._inv is None
@property
def inverse(self):
"""The inverse of this bidict.
*See also* :attr:`inv`
"""
# Resolve and return a strong reference to the inverse bidict.
# One may be stored in self._inv already.
if self._inv is not None:
return self._inv
# Otherwise a weakref is stored in self._invweak. Try to get a strong ref from it.
inv = self._invweak() # pylint: disable=not-callable
if inv is not None:
return inv
# Refcount of referent must have dropped to zero, as in `bidict().inv.inv`. Init a new one.
self._init_inv() # Now this bidict will retain a strong ref to its inverse.
return self._inv
@property
def inv(self):
"""Alias for :attr:`inverse`."""
return self.inverse
[docs] def __getstate__(self):
"""Needed to enable pickling due to use of :attr:`__slots__` and weakrefs.
*See also* :meth:`object.__getstate__`
"""
state = {}
for cls in self.__class__.__mro__:
slots = getattr(cls, '__slots__', ())
for slot in slots:
if hasattr(self, slot):
state[slot] = getattr(self, slot)
# weakrefs can't be pickled.
state.pop('_invweak', None) # Added back in __setstate__ via _init_inv call.
state.pop('__weakref__', None) # Not added back in __setstate__. Python manages this one.
return state
[docs] def __setstate__(self, state):
"""Implemented because use of :attr:`__slots__` would prevent unpickling otherwise.
*See also* :meth:`object.__setstate__`
"""
for slot, value in state.items():
setattr(self, slot, value)
self._init_inv()
[docs] def __repr__(self):
"""See :func:`repr`."""
clsname = self.__class__.__name__
if not self:
return '%s()' % clsname
return '%s(%r)' % (clsname, self._repr_delegate(self.items()))
# The inherited Mapping.__eq__ implementation would work, but it's implemented in terms of an
# inefficient ``dict(self.items()) == dict(other.items())`` comparison, so override it with a
# more efficient implementation.
[docs] def __eq__(self, other):
"""*x.__eq__(other) ⟺ x == other*
Equivalent to *dict(x.items()) == dict(other.items())*
but more efficient.
Note that :meth:`bidict's __eq__() <bidict.bidict.__eq__>` implementation
is inherited by subclasses,
in particular by the ordered bidict subclasses,
so even with ordered bidicts,
:ref:`== comparison is order-insensitive <eq-order-insensitive>`.
*See also* :meth:`bidict.FrozenOrderedBidict.equals_order_sensitive`
"""
if not isinstance(other, Mapping) or len(self) != len(other):
return False
selfget = self.get
return all(selfget(k, _MISS) == v for (k, v) in other.items())
# The following methods are mutating and so are not public. But they are implemented in this
# non-mutable base class (rather than the mutable `bidict` subclass) because they are used here
# during initialization (starting with the `_update` method). (Why is this? Because `__init__`
# and `update` share a lot of the same behavior (inserting the provided items while respecting
# `on_dup`), so it makes sense for them to share implementation too.)
def _pop(self, key):
val = self._fwdm.pop(key)
del self._invm[val]
return val
def _put(self, key, val, on_dup):
dedup_result = self._dedup_item(key, val, on_dup)
if dedup_result is not _NOOP:
self._write_item(key, val, dedup_result)
def _dedup_item(self, key, val, on_dup): # pylint: disable=too-many-branches
"""Check *key* and *val* for any duplication in self.
Handle any duplication as per the passed in *on_dup*.
(key, val) already present is construed as a no-op, not a duplication.
If duplication is found and the corresponding :class:`~bidict.OnDupAction` is
:attr:`~bidict.DROP_NEW`, return :obj:`_NOOP`.
If duplication is found and the corresponding :class:`~bidict.OnDupAction` is
:attr:`~bidict.RAISE`, raise the appropriate error.
If duplication is found and the corresponding :class:`~bidict.OnDupAction` is
:attr:`~bidict.DROP_OLD`,
or if no duplication is found,
return the :class:`_DedupResult` *(isdupkey, isdupval, oldkey, oldval)*.
"""
fwdm = self._fwdm
invm = self._invm
oldval = fwdm.get(key, _MISS)
oldkey = invm.get(val, _MISS)
isdupkey = oldval is not _MISS
isdupval = oldkey is not _MISS
dedup_result = _DedupResult(isdupkey, isdupval, oldkey, oldval)
if isdupkey and isdupval:
if self._already_have(key, val, oldkey, oldval):
# (key, val) duplicates an existing item -> no-op.
return _NOOP
# key and val each duplicate a different existing item.
if on_dup.kv is RAISE:
raise KeyAndValueDuplicationError(key, val)
if on_dup.kv is DROP_NEW:
return _NOOP
if on_dup.kv is not DROP_OLD: # pragma: no cover
raise ValueError(on_dup.kv)
# Fall through to the return statement on the last line.
elif isdupkey:
if on_dup.key is RAISE:
raise KeyDuplicationError(key)
if on_dup.key is DROP_NEW:
return _NOOP
if on_dup.key is not DROP_OLD: # pragma: no cover
raise ValueError(on_dup.key)
# Fall through to the return statement on the last line.
elif isdupval:
if on_dup.val is RAISE:
raise ValueDuplicationError(val)
if on_dup.val is DROP_NEW:
return _NOOP
if on_dup.val is not DROP_OLD: # pragma: no cover
raise ValueError(on_dup.val)
# Fall through to the return statement on the last line.
# else neither isdupkey nor isdupval.
return dedup_result
@staticmethod
def _already_have(key, val, oldkey, oldval):
# Overridden by _orderedbase.OrderedBidictBase.
isdup = oldkey == key
assert isdup == (oldval == val), '%r %r %r %r' % (key, val, oldkey, oldval)
return isdup
def _write_item(self, key, val, dedup_result):
# Overridden by _orderedbase.OrderedBidictBase.
isdupkey, isdupval, oldkey, oldval = dedup_result
fwdm = self._fwdm
invm = self._invm
fwdm[key] = val
invm[val] = key
if isdupkey:
del invm[oldval]
if isdupval:
del fwdm[oldkey]
return _WriteResult(key, val, oldkey, oldval)
def _update(self, init, on_dup, *args, **kw):
# args[0] may be a generator that yields many items, so process input in a single pass.
if not args and not kw:
return
can_skip_dup_check = not self and not kw and isinstance(args[0], BidirectionalMapping)
if can_skip_dup_check:
self._update_no_dup_check(args[0])
return
can_skip_rollback = init or RAISE not in on_dup
if can_skip_rollback:
self._update_no_rollback(on_dup, *args, **kw)
else:
self._update_with_rollback(on_dup, *args, **kw)
def _update_no_dup_check(self, other):
write_item = self._write_item
for (key, val) in other.items():
write_item(key, val, _NODUP)
def _update_no_rollback(self, on_dup, *args, **kw):
put = self._put
for (key, val) in _iteritems_args_kw(*args, **kw):
put(key, val, on_dup)
def _update_with_rollback(self, on_dup, *args, **kw):
"""Update, rolling back on failure."""
writelog = []
appendlog = writelog.append
dedup_item = self._dedup_item
write_item = self._write_item
for (key, val) in _iteritems_args_kw(*args, **kw):
try:
dedup_result = dedup_item(key, val, on_dup)
except DuplicationError:
undo_write = self._undo_write
for dedup_result, write_result in reversed(writelog):
undo_write(dedup_result, write_result)
raise
if dedup_result is not _NOOP:
write_result = write_item(key, val, dedup_result)
appendlog((dedup_result, write_result))
def _undo_write(self, dedup_result, write_result):
isdupkey, isdupval, _, _ = dedup_result
key, val, oldkey, oldval = write_result
if not isdupkey and not isdupval:
self._pop(key)
return
fwdm = self._fwdm
invm = self._invm
if isdupkey:
fwdm[key] = oldval
invm[oldval] = key
if not isdupval:
del invm[val]
if isdupval:
invm[val] = oldkey
fwdm[oldkey] = val
if not isdupkey:
del fwdm[key]
[docs] def copy(self):
"""A shallow copy."""
# Could just ``return self.__class__(self)`` here instead, but the below is faster. It uses
# __new__ to create a copy instance while bypassing its __init__, which would result
# in copying this bidict's items into the copy instance one at a time. Instead, make whole
# copies of each of the backing mappings, and make them the backing mappings of the copy,
# avoiding copying items one at a time.
cp = self.__class__.__new__(self.__class__) # pylint: disable=invalid-name
cp._fwdm = copy(self._fwdm) # pylint: disable=protected-access
cp._invm = copy(self._invm) # pylint: disable=protected-access
cp._init_inv() # pylint: disable=protected-access
return cp
[docs] def __copy__(self):
"""Used for the copy protocol.
*See also* the :mod:`copy` module
"""
return self.copy()
[docs] def __len__(self):
"""The number of contained items."""
return len(self._fwdm)
[docs] def __iter__(self): # lgtm [py/inheritance/incorrect-overridden-signature]
"""Iterator over the contained keys."""
# No default implementation for __iter__ inherited from Mapping ->
# always delegate to _fwdm.
return iter(self._fwdm)
[docs] def __getitem__(self, key):
"""*x.__getitem__(key) ⟺ x[key]*"""
return self._fwdm[key]
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