/* Ordered Dictionary object implementation.

This implementation is necessarily explicitly equivalent to the pure Python

OrderedDict class in Lib/collections/__init__.py. The strategy there

involves using a doubly-linked-list to capture the order. We keep to that

strategy, using a lower-level linked-list.

About the Linked-List

=====================

For the linked list we use a basic doubly-linked-list. Using a circularly-

linked-list does have some benefits, but they don't apply so much here

since OrderedDict is focused on the ends of the list (for the most part).

Furthermore, there are some features of generic linked-lists that we simply

don't need for OrderedDict. Thus a simple custom implementation meets our

needs. Alternatives to our simple approach include the QCIRCLE_*

macros from BSD's queue.h, and the linux's list.h.

Getting O(1) Node Lookup

------------------------

One invariant of Python's OrderedDict is that it preserves time complexity

of dict's methods, particularly the O(1) operations. Simply adding a

linked-list on top of dict is not sufficient here; operations for nodes in

the middle of the linked-list implicitly require finding the node first.

With a simple linked-list like we're using, that is an O(n) operation.

Consequently, methods like __delitem__() would change from O(1) to O(n),

which is unacceptable.

In order to preserve O(1) performance for node removal (finding nodes), we

must do better than just looping through the linked-list. Here are options

we've considered:

1. use a second dict to map keys to nodes (a la the pure Python version).

2. keep a simple hash table mirroring the order of dict's, mapping each key

to the corresponding node in the linked-list.

3. use a version of shared keys (split dict) that allows non-unicode keys.

4. have the value stored for each key be a (value, node) pair, and adjust

__getitem__(), get(), etc. accordingly.

The approach with the least performance impact (time and space) is #2,

mirroring the key order of dict's dk_enties with an array of node pointers.

While lookdict() and friends (dk_lookup) don't give us the index into the

array, we make use of pointer arithmetic to get that index. An alternative

would be to refactor lookdict() to provide the index, explicitly exposing

the implementation detail. We could even just use a custom lookup function

for OrderedDict that facilitates our need. However, both approaches are

significantly more complicated than just using pointer arithmetic.

The catch with mirroring the hash table ordering is that we have to keep

the ordering in sync through any dict resizes. However, that order only

matters during node lookup. We can simply defer any potential resizing

until we need to do a lookup.

Linked-List Nodes

-----------------

The current implementation stores a pointer to the associated key only.

One alternative would be to store a pointer to the PyDictKeyEntry instead.

This would save one pointer de-reference per item, which is nice during

calls to values() and items(). However, it adds unnecessary overhead

otherwise, so we stick with just the key.

Linked-List API

---------------

As noted, the linked-list implemented here does not have all the bells and

whistles. However, we recognize that the implementation may need to

change to accommodate performance improvements or extra functionality. To

that end, We use a simple API to interact with the linked-list. Here's a

summary of the methods/macros:

Node info:

* _odictnode_KEY(node)

* _odictnode_VALUE(od, node)

* _odictnode_PREV(node)

* _odictnode_NEXT(node)

Linked-List info:

* _odict_FIRST(od)

* _odict_LAST(od)

* _odict_EMPTY(od)

* _odict_FOREACH(od, node) - used in place of `for (node=...)`

For adding nodes:

* _odict_add_head(od, node)

* _odict_add_tail(od, node)

* _odict_add_new_node(od, key, hash)

For removing nodes:

* _odict_clear_node(od, node, key, hash)

* _odict_clear_nodes(od, clear_each)

Others:

* _odict_find_node_hash(od, key, hash)

* _odict_find_node(od, key)

* _odict_keys_equal(od1, od2)

Used, but specific to the linked-list implementation:

* _odict_free_fast_nodes(od)

And here's a look at how the linked-list relates to the OrderedDict API:

============ === === ==== ==== ==== === ==== ===== ==== ==== === ==== === ===

method key val prev next mem 1st last empty iter find add rmv clr keq

============ === === ==== ==== ==== === ==== ===== ==== ==== === ==== === ===

__del__ ~ X

__delitem__ free ~ node

__eq__ ~ X

__iter__ X X

__new__ X X

__reduce__ X ~ X

__repr__ X X X

__reversed__ X X

__setitem__ key

__sizeof__ size X

clear ~ ~ X

copy X X X

items X X X

keys X X

move_to_end X X X ~ h/t key

pop free key

popitem X X free X X node

setdefault ~ ? ~

values X X

============ === === ==== ==== ==== === ==== ===== ==== ==== === ==== === ===

__delitem__ is the only method that directly relies on finding an arbitrary

node in the linked-list. Everything else is iteration or relates to the

ends of the linked-list.

Situation that Endangers Consistency

------------------------------------

Using a raw linked-list for OrderedDict exposes a key situation that can

cause problems. If a node is stored in a variable, there is a chance that

the node may have been deallocated before the variable gets used, thus

potentially leading to a segmentation fault. A key place where this shows

up is during iteration through the linked list (via _odict_FOREACH or

otherwise).

A number of solutions are available to resolve this situation:

* defer looking up the node until as late as possible and certainly after

any code that could possibly result in a deletion;

* if the node is needed both before and after a point where the node might

be removed, do a check before using the node at the "after" location to

see if the node is still valid;

* like the last one, but simply pull the node again to ensure it's right;

* keep the key in the variable instead of the node and then look up the

node using the key at the point where the node is needed (this is what

we do for the iterators).

Another related problem, preserving consistent ordering during iteration,

is described below. That one is not exclusive to using linked-lists.

Challenges from Subclassing dict

================================

OrderedDict subclasses dict, which is an unusual relationship between two

builtin types (other than the base object type). Doing so results in

some complication and deserves further explanation. There are two things

to consider here. First, in what circumstances or with what adjustments

can OrderedDict be used as a drop-in replacement for dict (at the C level)?

Second, how can the OrderedDict implementation leverage the dict

implementation effectively without introducing unnecessary coupling or

inefficiencies?

This second point is reflected here and in the implementation, so the

further focus is on the first point. It is worth noting that for

overridden methods, the dict implementation is deferred to as much as

possible. Furthermore, coupling is limited to as little as is reasonable.

Concrete API Compatibility

--------------------------

Use of the concrete C-API for dict (PyDict_*) with OrderedDict is

problematic. (See http://bugs.python.org/issue10977.) The concrete API

has a number of hard-coded assumptions tied to the dict implementation.

This is, in part, due to performance reasons, which is understandable

given the part dict plays in Python.

Any attempt to replace dict with OrderedDict for any role in the

interpreter (e.g. **kwds) faces a challenge. Such any effort must

recognize that the instances in affected locations currently interact with

the concrete API.

Here are some ways to address this challenge:

1. Change the relevant usage of the concrete API in CPython and add

PyDict_CheckExact() calls to each of the concrete API functions.

2. Adjust the relevant concrete API functions to explicitly accommodate

OrderedDict.

3. As with #1, add the checks, but improve the abstract API with smart fast

paths for dict and OrderedDict, and refactor CPython to use the abstract

API. Improvements to the abstract API would be valuable regardless.

Adding the checks to the concrete API would help make any interpreter

switch to OrderedDict less painful for extension modules. However, this

won't work. The equivalent C API call to `dict.__setitem__(obj, k, v)`

is 'PyDict_SetItem(obj, k, v)`. This illustrates how subclasses in C call

the base class's methods, since there is no equivalent of super() in the

C API. Calling into Python for parent class API would work, but some

extension modules already rely on this feature of the concrete API.

For reference, here is a breakdown of some of the dict concrete API:

========================== ============= =======================

concrete API uses abstract API

========================== ============= =======================

PyDict_Check PyMapping_Check

(PyDict_CheckExact) -

(PyDict_New) -

(PyDictProxy_New) -

PyDict_Clear -

PyDict_Contains PySequence_Contains

PyDict_Copy -

PyDict_SetItem PyObject_SetItem

PyDict_SetItemString PyMapping_SetItemString

PyDict_DelItem PyMapping_DelItem

PyDict_DelItemString PyMapping_DelItemString

PyDict_GetItem -

PyDict_GetItemWithError PyObject_GetItem

_PyDict_GetItemIdWithError -

PyDict_GetItemString PyMapping_GetItemString

PyDict_Items PyMapping_Items

PyDict_Keys PyMapping_Keys

PyDict_Values PyMapping_Values

PyDict_Size PyMapping_Size

PyMapping_Length

PyDict_Next PyIter_Next

_PyDict_Next -

PyDict_Merge -

PyDict_Update -

PyDict_MergeFromSeq2 -

PyDict_ClearFreeList -

- PyMapping_HasKeyString

- PyMapping_HasKey

========================== ============= =======================

The dict Interface Relative to OrderedDict

==========================================

Since OrderedDict subclasses dict, understanding the various methods and

attributes of dict is important for implementing OrderedDict.

Relevant Type Slots

-------------------

================= ================ =================== ================

slot attribute object dict

================= ================ =================== ================

tp_dealloc - object_dealloc dict_dealloc

tp_repr __repr__ object_repr dict_repr

sq_contains __contains__ - dict_contains

mp_length __len__ - dict_length

mp_subscript __getitem__ - dict_subscript

mp_ass_subscript __setitem__ - dict_ass_sub

__delitem__

tp_hash __hash__ _Py_HashPointer ..._HashNotImpl

tp_str __str__ object_str -

tp_getattro __getattribute__ ..._GenericGetAttr (repeated)

__getattr__

tp_setattro __setattr__ ..._GenericSetAttr (disabled)

tp_doc __doc__ (literal) dictionary_doc

tp_traverse - - dict_traverse

tp_clear - - dict_tp_clear

tp_richcompare __eq__ object_richcompare dict_richcompare

__ne__

tp_weaklistoffset (__weakref__) - -

tp_iter __iter__ - dict_iter

tp_dictoffset (__dict__) - -

tp_init __init__ object_init dict_init

tp_alloc - PyType_GenericAlloc (repeated)

tp_new __new__ object_new dict_new

tp_free - PyObject_Del PyObject_GC_Del

================= ================ =================== ================

Relevant Methods

----------------

================ =================== ===============

method object dict

================ =================== ===============

__reduce__ object_reduce -

__sizeof__ object_sizeof dict_sizeof

clear - dict_clear

copy - dict_copy

fromkeys - dict_fromkeys

get - dict_get

items - dictitems_new

keys - dictkeys_new

pop - dict_pop

popitem - dict_popitem

setdefault - dict_setdefault

update - dict_update

values - dictvalues_new

================ =================== ===============

Pure Python OrderedDict

=======================

As already noted, compatibility with the pure Python OrderedDict

implementation is a key goal of this C implementation. To further that

goal, here's a summary of how OrderedDict-specific methods are implemented

in collections/__init__.py. Also provided is an indication of which

methods directly mutate or iterate the object, as well as any relationship

with the underlying linked-list.

============= ============== == ================ === === ====

method impl used ll uses inq mut iter

============= ============== == ================ === === ====

__contains__ dict - - X

__delitem__ OrderedDict Y dict.__delitem__ X

__eq__ OrderedDict N OrderedDict ~

dict.__eq__

__iter__

__getitem__ dict - - X

__iter__ OrderedDict Y - X

__init__ OrderedDict N update

__len__ dict - - X

__ne__ MutableMapping - __eq__ ~

__reduce__ OrderedDict N OrderedDict ~

__iter__

__getitem__

__repr__ OrderedDict N __class__ ~

items

__reversed__ OrderedDict Y - X

__setitem__ OrderedDict Y __contains__ X

dict.__setitem__

__sizeof__ OrderedDict Y __len__ ~

__dict__

clear OrderedDict Y dict.clear X

copy OrderedDict N __class__

__init__

fromkeys OrderedDict N __setitem__

get dict - - ~

items MutableMapping - ItemsView X

keys MutableMapping - KeysView X

move_to_end OrderedDict Y - X

pop OrderedDict N __contains__ X

__getitem__

__delitem__

popitem OrderedDict Y dict.pop X

setdefault OrderedDict N __contains__ ~

__getitem__

__setitem__

update MutableMapping - __setitem__ ~

values MutableMapping - ValuesView X

============= ============== == ================ === === ====

__reversed__ and move_to_end are both exclusive to OrderedDict.

C OrderedDict Implementation

============================

================= ================

slot impl

================= ================

tp_dealloc odict_dealloc

tp_repr odict_repr

mp_ass_subscript odict_ass_sub

tp_doc odict_doc

tp_traverse odict_traverse

tp_clear odict_tp_clear

tp_richcompare odict_richcompare

tp_weaklistoffset (offset)

tp_iter odict_iter

tp_dictoffset (offset)

tp_init odict_init

tp_alloc (repeated)

tp_new odict_new

================= ================

================= ================

method impl

================= ================

__reduce__ odict_reduce

__sizeof__ odict_sizeof

clear odict_clear

copy odict_copy

fromkeys odict_fromkeys

items odictitems_new

keys odictkeys_new

pop odict_pop

popitem odict_popitem

setdefault odict_setdefault

update odict_update

values odictvalues_new

================= ================

Inherited unchanged from object/dict:

================ ==========================

method type field

================ ==========================

- tp_free

__contains__ tp_as_sequence.sq_contains

__getattr__ tp_getattro

__getattribute__ tp_getattro

__getitem__ tp_as_mapping.mp_subscript

__hash__ tp_hash

__len__ tp_as_mapping.mp_length

__setattr__ tp_setattro

__str__ tp_str

get -

================ ==========================

Other Challenges

================

Preserving Ordering During Iteration

------------------------------------

During iteration through an OrderedDict, it is possible that items could

get added, removed, or reordered. For a linked-list implementation, as

with some other implementations, that situation may lead to undefined

behavior. The documentation for dict mentions this in the `iter()` section

of http://docs.python.org/3.4/library/stdtypes.html#dictionary-view-objects.

In this implementation we follow dict's lead (as does the pure Python

implementation) for __iter__(), keys(), values(), and items().

For internal iteration (using _odict_FOREACH or not), there is still the

risk that not all nodes that we expect to be seen in the loop actually get

seen. Thus, we are careful in each of those places to ensure that they

are. This comes, of course, at a small price at each location. The

solutions are much the same as those detailed in the `Situation that

Endangers Consistency` section above.

Potential Optimizations

=======================

* Allocate the nodes as a block via od_fast_nodes instead of individually.

- Set node->key to NULL to indicate the node is not-in-use.

- Add _odict_EXISTS()?

- How to maintain consistency across resizes? Existing node pointers

would be invalidate after a resize, which is particularly problematic

for the iterators.

* Use a more stream-lined implementation of update() and, likely indirectly,

__init__().

*/

/* TODO

sooner:

- reentrancy (make sure everything is at a thread-safe state when calling

into Python). I've already checked this multiple times, but want to

make one more pass.

- add unit tests for reentrancy?

later:

- make the dict views support the full set API (the pure Python impl does)

- implement a fuller MutableMapping API in C?

- move the MutableMapping implementation to abstract.c?

- optimize mutablemapping_update

- use PyObject_MALLOC (small object allocator) for odict nodes?

- support subclasses better (e.g. in odict_richcompare)

*/

#include "Python.h"

#include "structmember.h"

#include "dict-common.h"

#include <stddef.h>

typedef struct _odictnode _ODictNode;

/* PyODictObject */

struct _odictobject {

PyDictObject od_dict; /* the underlying dict */

_ODictNode *od_first; /* first node in the linked list, if any */

_ODictNode *od_last; /* last node in the linked list, if any */

/* od_fast_nodes, od_fast_nodes_size and od_resize_sentinel are managed

* by _odict_resize().

* Note that we rely on implementation details of dict for both. */

_ODictNode **od_fast_nodes; /* hash table that mirrors the dict table */

Py_ssize_t od_fast_nodes_size;

void *od_resize_sentinel; /* changes if odict should be resized */

size_t od_state; /* incremented whenever the LL changes */

PyObject *od_inst_dict; /* OrderedDict().__dict__ */

PyObject *od_weakreflist; /* holds weakrefs to the odict */

};

/* ----------------------------------------------

* odict keys (a simple doubly-linked list)

*/

struct _odictnode {

PyObject *key;

Py_hash_t hash;

_ODictNode *next;

_ODictNode *prev;

};

#define _odictnode_KEY(node) \

(node->key)

#define _odictnode_HASH(node) \

(node->hash)

/* borrowed reference */

#define _odictnode_VALUE(node, od) \

PyODict_GetItemWithError((PyObject *)od, _odictnode_KEY(node))

#define _odictnode_PREV(node) (node->prev)

#define _odictnode_NEXT(node) (node->next)

#define _odict_FIRST(od) (((PyODictObject *)od)->od_first)

#define _odict_LAST(od) (((PyODictObject *)od)->od_last)

#define _odict_EMPTY(od) (_odict_FIRST(od) == NULL)

#define _odict_FOREACH(od, node) \

for (node = _odict_FIRST(od); node != NULL; node = _odictnode_NEXT(node))

#define _odict_FAST_SIZE(od) ((PyDictObject *)od)->ma_keys->dk_size

static void

_odict_free_fast_nodes(PyODictObject *od) {

if (od->od_fast_nodes) {

PyMem_FREE(od->od_fast_nodes);

}

}

/* Return the index into the hash table, regardless of a valid node. */

static Py_ssize_t

_odict_get_index_raw(PyODictObject *od, PyObject *key, Py_hash_t hash)

{

PyObject **value_addr = NULL;

PyDictKeyEntry *ep;

PyDictKeysObject *keys = ((PyDictObject *)od)->ma_keys;

ep = (keys->dk_lookup)((PyDictObject *)od, key, hash, &value_addr);

if (ep == NULL)

return -1;

/* We use pointer arithmetic to get the entry's index into the table. */

return ep - keys->dk_entries;

}

/* Replace od->od_fast_nodes with a new table matching the size of dict's. */

static int

_odict_resize(PyODictObject *od) {

Py_ssize_t size, i;

_ODictNode **fast_nodes, *node;

/* Initialize a new "fast nodes" table. */

size = ((PyDictObject *)od)->ma_keys->dk_size;

fast_nodes = PyMem_NEW(_ODictNode *, size);

if (fast_nodes == NULL) {

PyErr_NoMemory();

return -1;

}

for (i = 0; i < size; i++)

fast_nodes[i] = NULL;

/* Copy the current nodes into the table. */

_odict_FOREACH(od, node) {

i = _odict_get_index_raw(od, _odictnode_KEY(node),

_odictnode_HASH(node));

if (i < 0) {

PyMem_FREE(fast_nodes);

return -1;

}

fast_nodes[i] = node;

}

/* Replace the old fast nodes table. */

_odict_free_fast_nodes(od);

od->od_fast_nodes = fast_nodes;

od->od_fast_nodes_size = size;

od->od_resize_sentinel = ((PyDictObject *)od)->ma_keys;

return 0;

}

/* Return the index into the hash table, regardless of a valid node. */

static Py_ssize_t

_odict_get_index(PyODictObject *od, PyObject *key, Py_hash_t hash)

{

PyDictKeysObject *keys;

assert(key != NULL);

keys = ((PyDictObject *)od)->ma_keys;

/* Ensure od_fast_nodes and dk_entries are in sync. */

if (od->od_resize_sentinel != keys ||

od->od_fast_nodes_size != keys->dk_size) {

int resize_res = _odict_resize(od);

if (resize_res < 0)

return -1;

}

return _odict_get_index_raw(od, key, hash);

}

/* Returns NULL if there was some error or the key was not found. */

static _ODictNode *

_odict_find_node_hash(PyODictObject *od, PyObject *key, Py_hash_t hash)

{

Py_ssize_t index;

if (_odict_EMPTY(od))

return NULL;

index = _odict_get_index(od, key, hash);

if (index < 0)

return NULL;

return od->od_fast_nodes[index];

}

static _ODictNode *

_odict_find_node(PyODictObject *od, PyObject *key)

{

Py_ssize_t index;

Py_hash_t hash;

if (_odict_EMPTY(od))

return NULL;

hash = PyObject_Hash(key);

if (hash == -1)

return NULL;

index = _odict_get_index(od, key, hash);

if (index < 0)

return NULL;

return od->od_fast_nodes[index];

}

static void

_odict_add_head(PyODictObject *od, _ODictNode *node)

{

_odictnode_PREV(node) = NULL;

_odictnode_NEXT(node) = _odict_FIRST(od);

if (_odict_FIRST(od) == NULL)

_odict_LAST(od) = node;

else

_odictnode_PREV(_odict_FIRST(od)) = node;

_odict_FIRST(od) = node;

od->od_state++;

}

static void

_odict_add_tail(PyODictObject *od, _ODictNode *node)

{

_odictnode_PREV(node) = _odict_LAST(od);

_odictnode_NEXT(node) = NULL;

if (_odict_LAST(od) == NULL)

_odict_FIRST(od) = node;

else

_odictnode_NEXT(_odict_LAST(od)) = node;

_odict_LAST(od) = node;

od->od_state++;

}

/* adds the node to the end of the list */

static int

_odict_add_new_node(PyODictObject *od, PyObject *key, Py_hash_t hash)

{

Py_ssize_t i;

_ODictNode *node;

Py_INCREF(key);

i = _odict_get_index(od, key, hash);

if (i < 0) {

if (!PyErr_Occurred())

PyErr_SetObject(PyExc_KeyError, key);

Py_DECREF(key);

return -1;

}

else if (od->od_fast_nodes[i] != NULL) {

/* We already have a node for the key so there's no need to add one. */

Py_DECREF(key);

return 0;

}

/* must not be added yet */

node = (_ODictNode *)PyMem_MALLOC(sizeof(_ODictNode));

if (node == NULL) {

Py_DECREF(key);

PyErr_NoMemory();

return -1;

}

_odictnode_KEY(node) = key;

_odictnode_HASH(node) = hash;

_odict_add_tail(od, node);

od->od_fast_nodes[i] = node;

return 0;

}

/* Putting the decref after the free causes problems. */

#define _odictnode_DEALLOC(node) \

do { \

Py_DECREF(_odictnode_KEY(node)); \

PyMem_FREE((void *)node); \

} while (0)

/* Repeated calls on the same node are no-ops. */

static void

_odict_remove_node(PyODictObject *od, _ODictNode *node)

{

if (_odict_FIRST(od) == node)

_odict_FIRST(od) = _odictnode_NEXT(node);

else if (_odictnode_PREV(node) != NULL)

_odictnode_NEXT(_odictnode_PREV(node)) = _odictnode_NEXT(node);

if (_odict_LAST(od) == node)

_odict_LAST(od) = _odictnode_PREV(node);

else if (_odictnode_NEXT(node) != NULL)

_odictnode_PREV(_odictnode_NEXT(node)) = _odictnode_PREV(node);

_odictnode_PREV(node) = NULL;

_odictnode_NEXT(node) = NULL;

od->od_state++;

}

/* If someone calls PyDict_DelItem() directly on an OrderedDict, we'll

get all sorts of problems here. In PyODict_DelItem we make sure to

call _odict_clear_node first.

This matters in the case of colliding keys. Suppose we add 3 keys:

[A, B, C], where the hash of C collides with A and the next possible

index in the hash table is occupied by B. If we remove B then for C

the dict's looknode func will give us the old index of B instead of

the index we got before deleting B. However, the node for C in

od_fast_nodes is still at the old dict index of C. Thus to be sure

things don't get out of sync, we clear the node in od_fast_nodes

*before* calling PyDict_DelItem.

The same must be done for any other OrderedDict operations where

we modify od_fast_nodes.

*/

static int

_odict_clear_node(PyODictObject *od, _ODictNode *node, PyObject *key,

Py_hash_t hash)

{

Py_ssize_t i;

assert(key != NULL);

if (_odict_EMPTY(od)) {

/* Let later code decide if this is a KeyError. */

return 0;

}

i = _odict_get_index(od, key, hash);

if (i < 0)

return PyErr_Occurred() ? -1 : 0;

if (node == NULL)

node = od->od_fast_nodes[i];

assert(node == od->od_fast_nodes[i]);

if (node == NULL) {

/* Let later code decide if this is a KeyError. */

return 0;

}

// Now clear the node.

od->od_fast_nodes[i] = NULL;

_odict_remove_node(od, node);

_odictnode_DEALLOC(node);

return 0;

}

static void

_odict_clear_nodes(PyODictObject *od)

{

_ODictNode *node, *next;

_odict_free_fast_nodes(od);

od->od_fast_nodes = NULL;

node = _odict_FIRST(od);

_odict_FIRST(od) = NULL;

_odict_LAST(od) = NULL;

while (node != NULL) {

next = _odictnode_NEXT(node);

_odictnode_DEALLOC(node);

node = next;

}

}

/* There isn't any memory management of nodes past this point. */

#undef _odictnode_DEALLOC

static int

_odict_keys_equal(PyODictObject *a, PyODictObject *b)

{

_ODictNode *node_a, *node_b;

node_a = _odict_FIRST(a);

node_b = _odict_FIRST(b);

while (1) {

if (node_a == NULL && node_b == NULL)

/* success: hit the end of each at the same time */

return 1;

else if (node_a == NULL || node_b == NULL)

/* unequal length */

return 0;

else {

int res = PyObject_RichCompareBool(

(PyObject *)_odictnode_KEY(node_a),

(PyObject *)_odictnode_KEY(node_b),

Py_EQ);

if (res < 0)

return res;

else if (res == 0)

return 0;

/* otherwise it must match, so move on to the next one */

node_a = _odictnode_NEXT(node_a);

node_b = _odictnode_NEXT(node_b);

}

}

}

/* ----------------------------------------------

* OrderedDict mapping methods

*/

/* mp_ass_subscript: __setitem__() and __delitem__() */

static int

odict_mp_ass_sub(PyODictObject *od, PyObject *v, PyObject *w)

{

if (w == NULL)

return PyODict_DelItem((PyObject *)od, v);

else

return PyODict_SetItem((PyObject *)od, v, w);

}

/* tp_as_mapping */

static PyMappingMethods odict_as_mapping = {

0, /*mp_length*/

0, /*mp_subscript*/

(objobjargproc)odict_mp_ass_sub, /*mp_ass_subscript*/

};

/* ----------------------------------------------

* OrderedDict methods

*/

/* __delitem__() */

PyDoc_STRVAR(odict_delitem__doc__, "od.__delitem__(y) <==> del od[y]");

/* __eq__() */

PyDoc_STRVAR(odict_eq__doc__,

"od.__eq__(y) <==> od==y. Comparison to another OD is order-sensitive \n\

while comparison to a regular mapping is order-insensitive.\n\

");

/* forward */

static PyObject * odict_richcompare(PyObject *v, PyObject *w, int op);

static PyObject *

odict_eq(PyObject *a, PyObject *b)

{

return odict_richcompare(a, b, Py_EQ);

}

/* __init__() */

PyDoc_STRVAR(odict_init__doc__,

"Initialize an ordered dictionary. The signature is the same as\n\

regular dictionaries, but keyword arguments are not recommended because\n\

their insertion order is arbitrary.\n\

\n\

");

/* forward */

static int odict_init(PyObject *self, PyObject *args, PyObject *kwds);

/* __iter__() */

PyDoc_STRVAR(odict_iter__doc__, "od.__iter__() <==> iter(od)");

static PyObject * odict_iter(PyODictObject *self); /* forward */

/* __ne__() */

/* Mapping.__ne__() does not have a docstring. */

PyDoc_STRVAR(odict_ne__doc__, "");

static PyObject *

odict_ne(PyObject *a, PyObject *b)

{

return odict_richcompare(a, b, Py_NE);

}

/* __repr__() */

PyDoc_STRVAR(odict_repr__doc__, "od.__repr__() <==> repr(od)");

static PyObject * odict_repr(PyODictObject *self); /* forward */

/* __setitem__() */

PyDoc_STRVAR(odict_setitem__doc__, "od.__setitem__(i, y) <==> od[i]=y");

/* fromkeys() */

PyDoc_STRVAR(odict_fromkeys__doc__,

"OD.fromkeys(S[, v]) -> New ordered dictionary with keys from S.\n\

If not specified, the value defaults to None.\n\

\n\

");

static PyObject *

odict_fromkeys(PyObject *cls, PyObject *args, PyObject *kwargs)

{

static char *kwlist[] = {"iterable", "value", 0};

PyObject *seq;

PyObject *value = Py_None;

/* both borrowed */

if (!PyArg_ParseTupleAndKeywords(args, kwargs, "O|O:fromkeys", kwlist,

&seq, &value)) {

return NULL;

}

return _PyDict_FromKeys(cls, seq, value);

}

/* __sizeof__() */

/* OrderedDict.__sizeof__() does not have a docstring. */

PyDoc_STRVAR(odict_sizeof__doc__, "");

static PyObject *

odict_sizeof(PyODictObject *od)

{

Py_ssize_t res = _PyDict_SizeOf((PyDictObject *)od);

res += sizeof(_ODictNode *) * _odict_FAST_SIZE(od); /* od_fast_nodes */

if (!_odict_EMPTY(od)) {

res += sizeof(_ODictNode) * PyODict_SIZE(od); /* linked-list */

}

return PyLong_FromSsize_t(res);

}

/* __reduce__() */

PyDoc_STRVAR(odict_reduce__doc__, "Return state information for pickling");

static PyObject *

odict_reduce(register PyODictObject *od)

{

_Py_IDENTIFIER(__dict__);

_Py_IDENTIFIER(items);

PyObject *dict = NULL, *result = NULL;

PyObject *items_iter, *items, *args = NULL;

/* capture any instance state */

dict = _PyObject_GetAttrId((PyObject *)od, &PyId___dict__);

if (dict == NULL)

goto Done;

else {

/* od.__dict__ isn't necessarily a dict... */

Py_ssize_t dict_len = PyObject_Length(dict);

if (dict_len == -1)

goto Done;

if (!dict_len) {

/* nothing to pickle in od.__dict__ */

Py_CLEAR(dict);

}

}

/* build the result */

args = PyTuple_New(0);

if (args == NULL)

goto Done;

items = _PyObject_CallMethodIdObjArgs((PyObject *)od, &PyId_items, NULL);

if (items == NULL)

goto Done;

items_iter = PyObject_GetIter(items);

Py_DECREF(items);

if (items_iter == NULL)

goto Done;

result = PyTuple_Pack(5, Py_TYPE(od), args, dict ? dict : Py_None, Py_None, items_iter);

Py_DECREF(items_iter);

Done:

Py_XDECREF(dict);

Py_XDECREF(args);

return result;

}

/* setdefault() */