After seeing requests for being able to access keys in a dictionary by value, the following recipe was born. It creates the DoubleDict class and allows just that. To ensure that only one key is returned when accessing it by value, values must be unique just as keys are unique, and this rule is automatically enforced. Most dictionary methods are supported, and many more are added to allow working with the dictionary from the view of the values instead of the keys. Several optional metaclasses are also provided to enable optional features in the DoubleDict class such as data consistency checks and atomic method execution.
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import threading
################################################################################
class _DDChecker(type):
def __new__(cls, name, bases, classdict):
for key, value in classdict.items():
if key not in {'__new__', '__slots__', '_DoubleDict__dict_view'}:
classdict[key] = cls._wrap(value)
return super().__new__(cls, name, bases, classdict)
@staticmethod
def _wrap(function):
@functools.wraps(function)
def check(self, *args, **kwargs):
value = function(self, *args, **kwargs)
if self._DoubleDict__forward != \
dict(map(reversed, self._DoubleDict__reverse.items())):
raise RuntimeError('Forward & Reverse are not equivalent!')
return value
return check
################################################################################
class _DDAtomic(_DDChecker):
def __new__(cls, name, bases, classdict):
if not bases:
classdict['__slots__'] += ('_DDAtomic__mutex',)
classdict['__new__'] = cls._atomic_new
return super().__new__(cls, name, bases, classdict)
@staticmethod
def _atomic_new(cls, iterable=(), **pairs):
instance = object.__new__(cls, iterable, **pairs)
instance.__mutex = threading.RLock()
instance.clear()
return instance
@staticmethod
def _wrap(function):
@functools.wraps(function)
def atomic(self, *args, **kwargs):
with self.__mutex:
return function(self, *args, **kwargs)
return atomic
################################################################################
class _DDAtomicChecker(_DDAtomic):
@staticmethod
def _wrap(function):
return _DDAtomic._wrap(_DDChecker._wrap(function))
################################################################################
class DoubleDict(metaclass=_DDAtomicChecker):
__slots__ = '__forward', '__reverse'
def __new__(cls, iterable=(), **pairs):
instance = super().__new__(cls, iterable, **pairs)
instance.clear()
return instance
def __init__(self, iterable=(), **pairs):
self.update(iterable, **pairs)
########################################################################
def __repr__(self):
return repr(self.__forward)
def __lt__(self, other):
return self.__forward < other
def __le__(self, other):
return self.__forward <= other
def __eq__(self, other):
return self.__forward == other
def __ne__(self, other):
return self.__forward != other
def __gt__(self, other):
return self.__forward > other
def __ge__(self, other):
return self.__forward >= other
def __len__(self):
return len(self.__forward)
def __getitem__(self, key):
if key in self:
return self.__forward[key]
return self.__missing_key(key)
def __setitem__(self, key, value):
if self.in_values(value):
del self[self.get_key(value)]
self.__set_key_value(key, value)
return value
def __delitem__(self, key):
self.pop(key)
def __iter__(self):
return iter(self.__forward)
def __contains__(self, key):
return key in self.__forward
########################################################################
def clear(self):
self.__forward = {}
self.__reverse = {}
def copy(self):
return self.__class__(self.items())
def del_value(self, value):
self.pop_key(value)
def get(self, key, default=None):
return self[key] if key in self else default
def get_key(self, value):
if self.in_values(value):
return self.__reverse[value]
return self.__missing_value(value)
def get_key_default(self, value, default=None):
return self.get_key(value) if self.in_values(value) else default
def in_values(self, value):
return value in self.__reverse
def items(self):
return self.__dict_view('items', ((key, self[key]) for key in self))
def iter_values(self):
return iter(self.__reverse)
def keys(self):
return self.__dict_view('keys', self.__forward)
def pop(self, key, *default):
if len(default) > 1:
raise TypeError('too many arguments')
if key in self:
value = self[key]
self.__del_key_value(key, value)
return value
if default:
return default[0]
raise KeyError(key)
def pop_key(self, value, *default):
if len(default) > 1:
raise TypeError('too many arguments')
if self.in_values(value):
key = self.get_key(value)
self.__del_key_value(key, value)
return key
if default:
return default[0]
raise KeyError(value)
def popitem(self):
try:
key = next(iter(self))
except StopIteration:
raise KeyError('popitem(): dictionary is empty')
return key, self.pop(key)
def set_key(self, value, key):
if key in self:
self.del_value(self[key])
self.__set_key_value(key, value)
return key
def setdefault(self, key, default=None):
if key not in self:
self[key] = default
return self[key]
def setdefault_key(self, value, default=None):
if not self.in_values(value):
self.set_key(value, default)
return self.get_key(value)
def update(self, iterable=(), **pairs):
for key, value in (((key, iterable[key]) for key in iterable.keys())
if hasattr(iterable, 'keys') else iterable):
self[key] = value
for key, value in pairs.items():
self[key] = value
def values(self):
return self.__dict_view('values', self.__reverse)
########################################################################
def __missing_key(self, key):
if hasattr(self.__class__, '__missing__'):
return self.__missing__(key)
if not hasattr(self, 'default_factory') \
or self.default_factory is None:
raise KeyError(key)
return self.__setitem__(key, self.default_factory())
def __missing_value(self, value):
if hasattr(self.__class__, '__missing_value__'):
return self.__missing_value__(value)
if not hasattr(self, 'default_key_factory') \
or self.default_key_factory is None:
raise KeyError(value)
return self.set_key(value, self.default_key_factory())
def __set_key_value(self, key, value):
self.__forward[key] = value
self.__reverse[value] = key
def __del_key_value(self, key, value):
del self.__forward[key]
del self.__reverse[value]
########################################################################
class __dict_view(frozenset):
__slots__ = '__name'
def __new__(cls, name, iterable=()):
instance = super().__new__(cls, iterable)
instance.__name = name
return instance
def __repr__(self):
return 'dict_{}({})'.format(self.__name, list(self))
|
The following test is a modified version of the standard library's dictionary test designed to work with this recipe.
from ddict import DoubleDict as dict
import unittest
from test import support
import collections, random, string
import gc, weakref
class DictTest(unittest.TestCase):
def test_invalid_keyword_arguments(self):
class Custom(dict):
pass
for invalid in {1 : 2}, Custom({1 : 2}):
with self.assertRaises(TypeError):
dict(**invalid)
with self.assertRaises(TypeError):
{}.update(**invalid)
def test_constructor(self):
# calling built-in types without argument must return empty
self.assertEqual(dict(), {})
self.assertIsNot(dict(), {})
def test_literal_constructor(self):
# check literal constructor for different sized dicts
# (to exercise the BUILD_MAP oparg).
for n in (0, 1, 6, 256, 400):
items = [(''.join(random.sample(string.ascii_letters, 8)), i)
for i in range(n)]
random.shuffle(items)
formatted_items = ('{!r}: {:d}'.format(k, v) for k, v in items)
dictliteral = '{' + ', '.join(formatted_items) + '}'
self.assertEqual(eval(dictliteral), dict(items))
def test_bool(self):
self.assertIs(not {}, True)
self.assertTrue({1: 2})
self.assertIs(bool({}), False)
self.assertIs(bool({1: 2}), True)
def test_keys(self):
d = {}
self.assertEqual(set(d.keys()), set())
d = {'a': 1, 'b': 2}
k = d.keys()
self.assertIn('a', d)
self.assertIn('b', d)
self.assertRaises(TypeError, d.keys, None)
self.assertEqual(repr(dict(a=1).keys()), "dict_keys(['a'])")
def test_values(self):
d = {}
self.assertEqual(set(d.values()), set())
d = {1:2}
self.assertEqual(set(d.values()), {2})
self.assertRaises(TypeError, d.values, None)
self.assertEqual(repr(dict(a=1).values()), "dict_values([1])")
def test_items(self):
d = {}
self.assertEqual(set(d.items()), set())
d = {1:2}
self.assertEqual(set(d.items()), {(1, 2)})
self.assertRaises(TypeError, d.items, None)
self.assertEqual(repr(dict(a=1).items()), "dict_items([('a', 1)])")
def test_contains(self):
d = {}
self.assertNotIn('a', d)
self.assertFalse('a' in d)
self.assertTrue('a' not in d)
d = {'a': 1, 'b': 2}
self.assertIn('a', d)
self.assertIn('b', d)
self.assertNotIn('c', d)
self.assertRaises(TypeError, d.__contains__)
def test_len(self):
d = {}
self.assertEqual(len(d), 0)
d = {'a': 1, 'b': 2}
self.assertEqual(len(d), 2)
def test_getitem(self):
d = {'a': 1, 'b': 2}
self.assertEqual(d['a'], 1)
self.assertEqual(d['b'], 2)
d['c'] = 3
d['a'] = 4
self.assertEqual(d['c'], 3)
self.assertEqual(d['a'], 4)
del d['b']
self.assertEqual(d, {'a': 4, 'c': 3})
self.assertRaises(TypeError, d.__getitem__)
class BadEq(object):
def __eq__(self, other):
raise Exc()
def __hash__(self):
return 24
d = {}
d[BadEq()] = 42
self.assertRaises(KeyError, d.__getitem__, 23)
class Exc(Exception): pass
class BadHash(object):
fail = False
def __hash__(self):
if self.fail:
raise Exc()
else:
return 42
x = BadHash()
d[x] = 42
x.fail = True
self.assertRaises(Exc, d.__getitem__, x)
def test_clear(self):
d = {1:1, 2:2, 3:3}
d.clear()
self.assertEqual(d, {})
self.assertRaises(TypeError, d.clear, None)
def test_update(self):
d = {}
d.update({1:100})
d.update({2:20})
d.update({1:1, 2:2, 3:3})
self.assertEqual(d, {1:1, 2:2, 3:3})
d.update()
self.assertEqual(d, {1:1, 2:2, 3:3})
self.assertRaises((TypeError, AttributeError), d.update, None)
class SimpleUserDict:
def __init__(self):
self.d = {1:1, 2:2, 3:3}
def keys(self):
return self.d.keys()
def __getitem__(self, i):
return self.d[i]
d.clear()
d.update(SimpleUserDict())
self.assertEqual(d, {1:1, 2:2, 3:3})
class Exc(Exception): pass
d.clear()
class FailingUserDict:
def keys(self):
raise Exc
self.assertRaises(Exc, d.update, FailingUserDict())
class FailingUserDict:
def keys(self):
class BogonIter:
def __init__(self):
self.i = 1
def __iter__(self):
return self
def __next__(self):
if self.i:
self.i = 0
return 'a'
raise Exc
return BogonIter()
def __getitem__(self, key):
return key
self.assertRaises(Exc, d.update, FailingUserDict())
class FailingUserDict:
def keys(self):
class BogonIter:
def __init__(self):
self.i = ord('a')
def __iter__(self):
return self
def __next__(self):
if self.i <= ord('z'):
rtn = chr(self.i)
self.i += 1
return rtn
raise StopIteration
return BogonIter()
def __getitem__(self, key):
raise Exc
self.assertRaises(Exc, d.update, FailingUserDict())
class badseq(object):
def __iter__(self):
return self
def __next__(self):
raise Exc()
self.assertRaises(Exc, {}.update, badseq())
self.assertRaises(ValueError, {}.update, [(1, 2, 3)])
def test_copy(self):
d = {1:1, 2:2, 3:3}
self.assertEqual(d.copy(), {1:1, 2:2, 3:3})
self.assertEqual({}.copy(), {})
self.assertRaises(TypeError, d.copy, None)
def test_get(self):
d = {}
self.assertIs(d.get('c'), None)
self.assertEqual(d.get('c', 3), 3)
d = {'a': 1, 'b': 2}
self.assertIs(d.get('c'), None)
self.assertEqual(d.get('c', 3), 3)
self.assertEqual(d.get('a'), 1)
self.assertEqual(d.get('a', 3), 1)
self.assertRaises(TypeError, d.get)
self.assertRaises(TypeError, d.get, None, None, None)
def test_setdefault(self):
# dict.setdefault()
d = {}
self.assertIs(d.setdefault('key0'), None)
d.setdefault('key0', [])
self.assertIs(d.setdefault('key0'), None)
d.setdefault('key', []).append(3)
self.assertEqual(d['key'][0], 3)
d.setdefault('key', []).append(4)
self.assertEqual(len(d['key']), 2)
self.assertRaises(TypeError, d.setdefault)
class Exc(Exception): pass
class BadHash(object):
fail = False
def __hash__(self):
if self.fail:
raise Exc()
else:
return 42
x = BadHash()
d[x] = 42
x.fail = True
self.assertRaises(Exc, d.setdefault, x, [])
def test_popitem(self):
# dict.popitem()
for copymode in -1, +1:
# -1: b has same structure as a
# +1: b is a.copy()
for log2size in range(12):
size = 2**log2size
a = {}
b = {}
for i in range(size):
a[repr(i)] = i
if copymode < 0:
b[repr(i)] = i
if copymode > 0:
b = a.copy()
for i in range(size):
ka, va = ta = a.popitem()
self.assertEqual(va, int(ka))
kb, vb = tb = b.popitem()
self.assertEqual(vb, int(kb))
self.assertFalse(copymode < 0 and ta != tb)
self.assertFalse(a)
self.assertFalse(b)
d = {}
self.assertRaises(KeyError, d.popitem)
def test_pop(self):
# Tests for pop with specified key
d = {}
k, v = 'abc', 'def'
d[k] = v
self.assertRaises(KeyError, d.pop, 'ghi')
self.assertEqual(d.pop(k), v)
self.assertEqual(len(d), 0)
self.assertRaises(KeyError, d.pop, k)
self.assertEqual(d.pop(k, v), v)
d[k] = v
self.assertEqual(d.pop(k, 1), v)
self.assertRaises(TypeError, d.pop)
class Exc(Exception): pass
class BadHash(object):
fail = False
def __hash__(self):
if self.fail:
raise Exc()
else:
return 42
x = BadHash()
d[x] = 42
x.fail = True
self.assertRaises(Exc, d.pop, x)
def test_mutatingiteration(self):
# changing dict size during iteration
d = {}
d[1] = 1
with self.assertRaises(RuntimeError):
for i in d:
d[i+1] = 1
def test_repr(self):
d = {}
self.assertEqual(repr(d), '{}')
d[1] = 2
self.assertEqual(repr(d), '{1: 2}')
d = {}
d[1] = d
self.assertEqual(repr(d), '{1: {...}}')
class Exc(Exception): pass
class BadRepr(object):
def __repr__(self):
raise Exc()
d = {1: BadRepr()}
self.assertRaises(Exc, repr, d)
def test_eq(self):
self.assertEqual({}, {})
self.assertEqual({1: 2}, {1: 2})
class Exc(Exception): pass
class BadCmp(object):
def __eq__(self, other):
raise Exc()
def __hash__(self):
return 1
d1 = {BadCmp(): 1}
d2 = {1: 1}
with self.assertRaises(Exc):
d1 == d2
def test_keys_contained(self):
self.helper_keys_contained(lambda x: x.keys())
self.helper_keys_contained(lambda x: x.items())
def helper_keys_contained(self, fn):
# Test rich comparisons against dict key views, which should behave the
# same as sets.
empty = fn(dict())
empty2 = fn(dict())
smaller = fn({1:1, 2:2})
larger = fn({1:1, 2:2, 3:3})
larger2 = fn({1:1, 2:2, 3:3})
larger3 = fn({4:1, 2:2, 3:3})
self.assertTrue(smaller < larger)
self.assertTrue(smaller <= larger)
self.assertTrue(larger > smaller)
self.assertTrue(larger >= smaller)
self.assertFalse(smaller >= larger)
self.assertFalse(smaller > larger)
self.assertFalse(larger <= smaller)
self.assertFalse(larger < smaller)
self.assertFalse(smaller < larger3)
self.assertFalse(smaller <= larger3)
self.assertFalse(larger3 > smaller)
self.assertFalse(larger3 >= smaller)
# Inequality strictness
self.assertTrue(larger2 >= larger)
self.assertTrue(larger2 <= larger)
self.assertFalse(larger2 > larger)
self.assertFalse(larger2 < larger)
self.assertTrue(larger == larger2)
self.assertTrue(smaller != larger)
# There is an optimization on the zero-element case.
self.assertTrue(empty == empty2)
self.assertFalse(empty != empty2)
self.assertFalse(empty == smaller)
self.assertTrue(empty != smaller)
# With the same size, an elementwise compare happens
self.assertTrue(larger != larger3)
self.assertFalse(larger == larger3)
def test_errors_in_view_containment_check(self):
class C:
def __eq__(self, other):
raise RuntimeError
d1 = {1: C()}
d2 = {1: C()}
with self.assertRaises(RuntimeError):
d1.items() == d2.items()
with self.assertRaises(RuntimeError):
d1.items() != d2.items()
with self.assertRaises(RuntimeError):
d1.items() <= d2.items()
with self.assertRaises(RuntimeError):
d1.items() >= d2.items()
d3 = {1: C(), 2: C()}
with self.assertRaises(RuntimeError):
d2.items() < d3.items()
with self.assertRaises(RuntimeError):
d3.items() > d2.items()
def test_dictview_set_operations_on_keys(self):
k1 = {1:1, 2:2}.keys()
k2 = {1:1, 2:2, 3:3}.keys()
k3 = {4:4}.keys()
self.assertEqual(k1 - k2, set())
self.assertEqual(k1 - k3, {1,2})
self.assertEqual(k2 - k1, {3})
self.assertEqual(k3 - k1, {4})
self.assertEqual(k1 & k2, {1,2})
self.assertEqual(k1 & k3, set())
self.assertEqual(k1 | k2, {1,2,3})
self.assertEqual(k1 ^ k2, {3})
self.assertEqual(k1 ^ k3, {1,2,4})
def test_dictview_set_operations_on_items(self):
k1 = {1:1, 2:2}.items()
k2 = {1:1, 2:2, 3:3}.items()
k3 = {4:4}.items()
self.assertEqual(k1 - k2, set())
self.assertEqual(k1 - k3, {(1,1), (2,2)})
self.assertEqual(k2 - k1, {(3,3)})
self.assertEqual(k3 - k1, {(4,4)})
self.assertEqual(k1 & k2, {(1,1), (2,2)})
self.assertEqual(k1 & k3, set())
self.assertEqual(k1 | k2, {(1,1), (2,2), (3,3)})
self.assertEqual(k1 ^ k2, {(3,3)})
self.assertEqual(k1 ^ k3, {(1,1), (2,2), (4,4)})
def test_dictview_mixed_set_operations(self):
# Just a few for .keys()
self.assertTrue({1:1}.keys() == {1})
self.assertTrue({1} == {1:1}.keys())
self.assertEqual({1:1}.keys() | {2}, {1, 2})
self.assertEqual({2} | {1:1}.keys(), {1, 2})
# And a few for .items()
self.assertTrue({1:1}.items() == {(1,1)})
self.assertTrue({(1,1)} == {1:1}.items())
self.assertEqual({1:1}.items() | {2}, {(1,1), 2})
self.assertEqual({2} | {1:1}.items(), {(1,1), 2})
def test_missing(self):
# Make sure dict doesn't have a __missing__ method
self.assertFalse(hasattr(dict, "__missing__"))
self.assertFalse(hasattr({}, "__missing__"))
# Test several cases:
# (D) subclass defines __missing__ method returning a value
# (E) subclass defines __missing__ method raising RuntimeError
# (F) subclass sets __missing__ instance variable (no effect)
# (G) subclass doesn't define __missing__ at a all
class D(dict):
def __missing__(self, key):
return 42
d = D({1: 2, 3: 4})
self.assertEqual(d[1], 2)
self.assertEqual(d[3], 4)
self.assertNotIn(2, d)
self.assertNotIn(2, d.keys())
self.assertEqual(d[2], 42)
class E(dict):
def __missing__(self, key):
raise RuntimeError(key)
e = E()
with self.assertRaises(RuntimeError) as c:
e[42]
self.assertEqual(c.exception.args, (42,))
class F(dict):
def __init__(self):
# An instance variable __missing__ should have no effect
self.__missing__ = lambda key: None
f = F()
with self.assertRaises(KeyError) as c:
f[42]
self.assertEqual(c.exception.args, (42,))
class G(dict):
pass
g = G()
with self.assertRaises(KeyError) as c:
g[42]
self.assertEqual(c.exception.args, (42,))
def test_tuple_keyerror(self):
# SF #1576657
d = {}
with self.assertRaises(KeyError) as c:
d[(1,)]
self.assertEqual(c.exception.args, ((1,),))
def test_bad_key(self):
# Dictionary lookups should fail if __eq__() raises an exception.
class CustomException(Exception):
pass
class BadDictKey:
def __hash__(self):
return hash(self.__class__)
def __eq__(self, other):
if isinstance(other, self.__class__):
raise CustomException
return other
d = {}
x1 = BadDictKey()
x2 = BadDictKey()
d[x1] = 1
for stmt in ['d[x2] = 2',
'z = d[x2]',
'x2 in d',
'd.get(x2)',
'd.setdefault(x2, 42)',
'd.pop(x2)',
'd.update({x2: 2})']:
with self.assertRaises(CustomException):
exec(stmt, locals())
def test_resize1(self):
# Dict resizing bug, found by Jack Jansen in 2.2 CVS development.
# This version got an assert failure in debug build, infinite loop in
# release build. Unfortunately, provoking this kind of stuff requires
# a mix of inserts and deletes hitting exactly the right hash codes in
# exactly the right order, and I can't think of a randomized approach
# that would be *likely* to hit a failing case in reasonable time.
d = {}
for i in range(5):
d[i] = i
for i in range(5):
del d[i]
for i in range(5, 9): # i==8 was the problem
d[i] = i
def test_resize2(self):
# Another dict resizing bug (SF bug #1456209).
# This caused Segmentation faults or Illegal instructions.
class X(object):
def __hash__(self):
return 5
def __eq__(self, other):
if resizing:
d.clear()
return False
d = {}
resizing = False
d[X()] = 1
d[X()] = 2
d[X()] = 3
d[X()] = 4
d[X()] = 5
# now trigger a resize
resizing = True
d[9] = 6
def test_empty_presized_dict_in_freelist(self):
# Bug #3537: if an empty but presized dict with a size larger
# than 7 was in the freelist, it triggered an assertion failure
with self.assertRaises(ZeroDivisionError):
d = {'a': 1 // 0, 'b': None, 'c': None, 'd': None, 'e': None,
'f': None, 'g': None, 'h': None}
d = {}
def test_container_iterator(self):
# Bug #3680: tp_traverse was not implemented for dictiter and
# dictview objects.
class C(object):
pass
views = (dict.items, dict.values, dict.keys)
for v in views:
obj = C()
ref = weakref.ref(obj)
container = dict({obj: 1})
obj.v = v(container)
obj.x = iter(obj.v)
del obj, container
gc.collect()
self.assertIs(ref(), None, "Cycle was not collected")
def _not_tracked(self, t):
# Nested containers can take several collections to untrack
gc.collect()
gc.collect()
self.assertFalse(gc.is_tracked(t), t)
def _tracked(self, t):
self.assertTrue(gc.is_tracked(t), t)
gc.collect()
gc.collect()
self.assertTrue(gc.is_tracked(t), t)
@support.cpython_only
def test_track_literals(self):
# Test GC-optimization of dict literals
x, y, z, w = 1.5, "a", (1, None), []
self._not_tracked({})
self._not_tracked({x:(), y:x, z:1})
self._not_tracked({1: "a", "b": 2})
self._not_tracked({1: 2, (None, True, False, ()): int})
self._not_tracked({1: object()})
# Dicts with mutable elements are always tracked, even if those
# elements are not tracked right now.
self._tracked({1: []})
self._tracked({1: ([],)})
self._tracked({1: {}})
self._tracked({1: set()})
@support.cpython_only
def test_track_subtypes(self):
# Dict subtypes are always tracked
class MyDict(dict):
pass
self._tracked(MyDict())
from test import mapping_tests
class GeneralMappingTests(mapping_tests.BasicTestMappingProtocol):
type2test = dict
class Dict(dict):
pass
class SubclassMappingTests(mapping_tests.BasicTestMappingProtocol):
type2test = Dict
def test_main():
support.run_unittest(
DictTest,
GeneralMappingTests,
SubclassMappingTests,
)
if __name__ == "__main__":
test_main()
Tags: class, dictionary
