PEP 372: OrderedDict()

Doc/library/collections.rst

@@ -14,7 +14,7 @@
    __name__ = '<doctest>'
 
 This module implements high-performance container datatypes.  Currently,
-there are three datatypes, :class:`Counter`, :class:`deque` and
+there are four datatypes, :class:`Counter`, :class:`deque`, :class:`OrderedDict` and
 :class:`defaultdict`, and one datatype factory function, :func:`namedtuple`.
 
 The specialized containers provided in this module provide alternatives
@@ -806,6 +806,33 @@ and more efficient to use a simple class declaration:
    adapted for Python 2.4.
 
 
+:class:`OrderedDict` objects
+----------------------------
+
+Ordered dictionaries are just like regular dictionaries but they remember the
+order that items were inserted.  When iterating over an ordered dictionary,
+the items are returned in the order their keys were first added.
+
+.. class:: OrderedDict([items])
+
+   Return an instance of a dict subclass, supporting the usual :class:`dict`
+   methods.  An *OrderedDict* is a dict that remembers the order that keys
+   were first inserted. If a new entry overwrites an existing entry, the
+   original insertion position is left unchanged.  Deleting an entry and
+   reinserting it will move it to the end.
+
+   .. versionadded:: 2.7
+
+The :meth:`popitem` method for ordered dictionaries returns and removes the
+last added entry.  The key/value pairs are returned in LIFO order.
+
+Equality tests between :class:`OrderedDict` objects are order-sensitive
+and are implemented as ``list(od1.items())==list(od2.items())``.
+Equality tests between :class:`OrderedDict` objects and other
+:class:`Mapping` objects are order-insensitive like regular dictionaries.
+This allows :class:`OrderedDict` objects to be substituted anywhere a
+regular dictionary is used.
+
 
 :class:`UserDict` objects
 -------------------------

Lib/collections.py

 __all__ = ['deque', 'defaultdict', 'namedtuple', 'UserDict', 'UserList',
-            'UserString', 'Counter']
+            'UserString', 'Counter', 'OrderedDict']
 # For bootstrapping reasons, the collection ABCs are defined in _abcoll.py.
 # They should however be considered an integral part of collections.py.
 from _abcoll import *
@@ -11,7 +11,81 @@ from operator import itemgetter as _itemgetter
 from keyword import iskeyword as _iskeyword
 import sys as _sys
 import heapq as _heapq
-from itertools import repeat as _repeat, chain as _chain, starmap as _starmap
+from itertools import repeat as _repeat, chain as _chain, starmap as _starmap, \
+                      zip_longest as _zip_longest
+
+################################################################################
+### OrderedDict
+################################################################################
+
+class OrderedDict(dict, MutableMapping):
+
+    def __init__(self, *args, **kwds):
+        if len(args) > 1:
+            raise TypeError('expected at most 1 arguments, got %d' % len(args))
+        if not hasattr(self, '_keys'):
+            self._keys = []
+        self.update(*args, **kwds)
+
+    def clear(self):
+        del self._keys[:]
+        dict.clear(self)
+
+    def __setitem__(self, key, value):
+        if key not in self:
+            self._keys.append(key)
+        dict.__setitem__(self, key, value)
+
+    def __delitem__(self, key):
+        dict.__delitem__(self, key)
+        self._keys.remove(key)
+
+    def __iter__(self):
+        return iter(self._keys)
+
+    def __reversed__(self):
+        return reversed(self._keys)
+
+    def popitem(self):
+        if not self:
+            raise KeyError('dictionary is empty')
+        key = self._keys.pop()
+        value = dict.pop(self, key)
+        return key, value
+
+    def __reduce__(self):
+        items = [[k, self[k]] for k in self]
+        inst_dict = vars(self).copy()
+        inst_dict.pop('_keys', None)
+        return (self.__class__, (items,), inst_dict)
+
+    setdefault = MutableMapping.setdefault
+    update = MutableMapping.update
+    pop = MutableMapping.pop
+    keys = MutableMapping.keys
+    values = MutableMapping.values
+    items = MutableMapping.items
+
+    def __repr__(self):
+        if not self:
+            return '%s()' % (self.__class__.__name__,)
+        return '%s(%r)' % (self.__class__.__name__, list(self.items()))
+
+    def copy(self):
+        return self.__class__(self)
+
+    @classmethod
+    def fromkeys(cls, iterable, value=None):
+        d = cls()
+        for key in iterable:
+            d[key] = value
+        return d
+
+    def __eq__(self, other):
+        if isinstance(other, OrderedDict):
+            return all(p==q for p, q in  _zip_longest(self.items(), other.items()))
+        return dict.__eq__(self, other)
+
 
 
 ################################################################################

Lib/test/test_collections.py

 """Unit tests for collections.py."""
 
 import unittest, doctest
+import inspect
 from test import support
-from collections import namedtuple, Counter, Mapping
+from collections import namedtuple, Counter, OrderedDict
+from test import mapping_tests
 import pickle, copy
-from random import randrange
+from random import randrange, shuffle
 import operator
 from collections import Hashable, Iterable, Iterator
 from collections import Sized, Container, Callable
@@ -571,12 +573,201 @@ class TestCounter(unittest.TestCase):
                 set_result = setop(set(p.elements()), set(q.elements()))
                 self.assertEqual(counter_result, dict.fromkeys(set_result, 1))
 
+
+class TestOrderedDict(unittest.TestCase):
+
+    def test_init(self):
+        with self.assertRaises(TypeError):
+            OrderedDict([('a', 1), ('b', 2)], None)                                 # too many args
+        pairs = [('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5)]
+        self.assertEqual(sorted(OrderedDict(dict(pairs)).items()), pairs)           # dict input
+        self.assertEqual(sorted(OrderedDict(**dict(pairs)).items()), pairs)         # kwds input
+        self.assertEqual(list(OrderedDict(pairs).items()), pairs)                   # pairs input
+        self.assertEqual(list(OrderedDict([('a', 1), ('b', 2), ('c', 9), ('d', 4)],
+                                          c=3, e=5).items()), pairs)                # mixed input
+
+        # make sure no positional args conflict with possible kwdargs
+        self.assertEqual(inspect.getargspec(OrderedDict.__dict__['__init__']).args,
+                         ['self'])
+
+        # Make sure that direct calls to __init__ do not clear previous contents
+        d = OrderedDict([('a', 1), ('b', 2), ('c', 3), ('d', 44), ('e', 55)])
+        d.__init__([('e', 5), ('f', 6)], g=7, d=4)
+        self.assertEqual(list(d.items()),
+            [('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5), ('f', 6), ('g', 7)])
+
+    def test_update(self):
+        with self.assertRaises(TypeError):
+            OrderedDict().update([('a', 1), ('b', 2)], None)                        # too many args
+        pairs = [('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5)]
+        od = OrderedDict()
+        od.update(dict(pairs))
+        self.assertEqual(sorted(od.items()), pairs)                                 # dict input
+        od = OrderedDict()
+        od.update(**dict(pairs))
+        self.assertEqual(sorted(od.items()), pairs)                                 # kwds input
+        od = OrderedDict()
+        od.update(pairs)
+        self.assertEqual(list(od.items()), pairs)                                   # pairs input
+        od = OrderedDict()
+        od.update([('a', 1), ('b', 2), ('c', 9), ('d', 4)], c=3, e=5)
+        self.assertEqual(list(od.items()), pairs)                                   # mixed input
+
+        # Make sure that direct calls to update do not clear previous contents
+        # add that updates items are not moved to the end
+        d = OrderedDict([('a', 1), ('b', 2), ('c', 3), ('d', 44), ('e', 55)])
+        d.update([('e', 5), ('f', 6)], g=7, d=4)
+        self.assertEqual(list(d.items()),
+            [('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5), ('f', 6), ('g', 7)])
+
+    def test_clear(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        shuffle(pairs)
+        od = OrderedDict(pairs)
+        self.assertEqual(len(od), len(pairs))
+        od.clear()
+        self.assertEqual(len(od), 0)
+
+    def test_delitem(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        od = OrderedDict(pairs)
+        del od['a']
+        self.assert_('a' not in od)
+        with self.assertRaises(KeyError):
+            del od['a']
+        self.assertEqual(list(od.items()), pairs[:2] + pairs[3:])
+
+    def test_setitem(self):
+        od = OrderedDict([('d', 1), ('b', 2), ('c', 3), ('a', 4), ('e', 5)])
+        od['c'] = 10           # existing element
+        od['f'] = 20           # new element
+        self.assertEqual(list(od.items()),
+                         [('d', 1), ('b', 2), ('c', 10), ('a', 4), ('e', 5), ('f', 20)])
+
+    def test_iterators(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        shuffle(pairs)
+        od = OrderedDict(pairs)
+        self.assertEqual(list(od), [t[0] for t in pairs])
+        self.assertEqual(list(od.keys()), [t[0] for t in pairs])
+        self.assertEqual(list(od.values()), [t[1] for t in pairs])
+        self.assertEqual(list(od.items()), pairs)
+        self.assertEqual(list(reversed(od)),
+                         [t[0] for t in reversed(pairs)])
+
+    def test_popitem(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        shuffle(pairs)
+        od = OrderedDict(pairs)
+        while pairs:
+            self.assertEqual(od.popitem(), pairs.pop())
+        with self.assertRaises(KeyError):
+            od.popitem()
+        self.assertEqual(len(od), 0)
+
+    def test_pop(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        shuffle(pairs)
+        od = OrderedDict(pairs)
+        shuffle(pairs)
+        while pairs:
+            k, v = pairs.pop()
+            self.assertEqual(od.pop(k), v)
+        with self.assertRaises(KeyError):
+            od.pop('xyz')
+        self.assertEqual(len(od), 0)
+        self.assertEqual(od.pop(k, 12345), 12345)
+
+    def test_equality(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        shuffle(pairs)
+        od1 = OrderedDict(pairs)
+        od2 = OrderedDict(pairs)
+        self.assertEqual(od1, od2)          # same order implies equality
+        pairs = pairs[2:] + pairs[:2]
+        od2 = OrderedDict(pairs)
+        self.assertNotEqual(od1, od2)       # different order implies inequality
+        # comparison to regular dict is not order sensitive
+        self.assertEqual(od1, dict(od2))
+        self.assertEqual(dict(od2), od1)
+        # different length implied inequality
+        self.assertNotEqual(od1, OrderedDict(pairs[:-1]))
+
+    def test_copying(self):
+        # Check that ordered dicts are copyable, deepcopyable, picklable,
+        # and have a repr/eval round-trip
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        od = OrderedDict(pairs)
+        update_test = OrderedDict()
+        update_test.update(od)
+        for i, dup in enumerate([
+                    od.copy(),
+                    copy.copy(od),
+                    copy.deepcopy(od),
+                    pickle.loads(pickle.dumps(od, 0)),
+                    pickle.loads(pickle.dumps(od, 1)),
+                    pickle.loads(pickle.dumps(od, 2)),
+                    pickle.loads(pickle.dumps(od, 3)),
+                    pickle.loads(pickle.dumps(od, -1)),
+                    eval(repr(od)),
+                    update_test,
+                    OrderedDict(od),
+                    ]):
+            self.assert_(dup is not od)
+            self.assertEquals(dup, od)
+            self.assertEquals(list(dup.items()), list(od.items()))
+            self.assertEquals(len(dup), len(od))
+            self.assertEquals(type(dup), type(od))
+
+    def test_repr(self):
+        od = OrderedDict([('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)])
+        self.assertEqual(repr(od),
+            "OrderedDict([('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)])")
+        self.assertEqual(eval(repr(od)), od)
+        self.assertEqual(repr(OrderedDict()), "OrderedDict()")
+
+    def test_setdefault(self):
+        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
+        shuffle(pairs)
+        od = OrderedDict(pairs)
+        pair_order = list(od.items())
+        self.assertEqual(od.setdefault('a', 10), 3)
+        # make sure order didn't change
+        self.assertEqual(list(od.items()), pair_order)
+        self.assertEqual(od.setdefault('x', 10), 10)
+        # make sure 'x' is added to the end
+        self.assertEqual(list(od.items())[-1], ('x', 10))
+
+    def test_reinsert(self):
+        # Given insert a, insert b, delete a, re-insert a,
+        # verify that a is now later than b.
+        od = OrderedDict()
+        od['a'] = 1
+        od['b'] = 2
+        del od['a']
+        od['a'] = 1
+        self.assertEqual(list(od.items()), [('b', 2), ('a', 1)])
+
+
+
+class GeneralMappingTests(mapping_tests.BasicTestMappingProtocol):
+    type2test = OrderedDict
+
+class MyOrderedDict(OrderedDict):
+    pass
+
+class SubclassMappingTests(mapping_tests.BasicTestMappingProtocol):
+    type2test = MyOrderedDict
+
+
+
 import doctest, collections
 
 def test_main(verbose=None):
     NamedTupleDocs = doctest.DocTestSuite(module=collections)
     test_classes = [TestNamedTuple, NamedTupleDocs, TestOneTrickPonyABCs,
-                    TestCollectionABCs, TestCounter]
+                    TestCollectionABCs, TestCounter,
+                    TestOrderedDict, GeneralMappingTests, SubclassMappingTests]
     support.run_unittest(*test_classes)
     support.run_doctest(collections, verbose)
 

Misc/NEWS

@@ -175,6 +175,8 @@ Core and Builtins
 Library
 -------
 
+- PEP 372:  Added collections.OrderedDict().
+
 - Issue #1733986: Fixed mmap crash in accessing elements of second map object
   with same tagname but larger size than first map. (Windows)