Source code for bidict._base

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# Copyright 2009-2020 Joshua Bronson. All Rights Reserved.
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"""Provides :class:`BidictBase`."""

from collections import namedtuple
from import Mapping
from copy import copy
from weakref import ref

from ._abc import BidirectionalMapping
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)

# Since BidirectionalMapping implements __subclasshook__, and BidictBase
# provides all the required attributes that the __subclasshook__ checks for,
# BidictBase would be a (virtual) subclass of BidirectionalMapping even if
# it didn't subclass it explicitly. But subclassing BidirectionalMapping
# explicitly allows BidictBase to inherit any useful implementations that
# BidirectionalMapping provides that aren't part of the required interface,
# such as its implementations of `__inverted__` and `values`.

[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:`` #: storing the forward mapping data (*key* → *value*). self._fwdm = self._fwdm_cls() #: The backing :class:`` #: 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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