-

cool-RR · cool-RR · commit e67bf069cba3 · 2013-10-26T01:09:43.000+03:00
diff --git a/source_py2/python_toolbox/nifty_collections/__init__.py b/source_py2/python_toolbox/nifty_collections/__init__.py
@@ -8,6 +8,7 @@
 from .weak_key_default_dict import WeakKeyDefaultDict
 from .weak_key_identity_dict import WeakKeyIdentityDict
 from .lazy_tuple import LazyTuple
+from .frozen_dict import FrozenDict
 
 from .emitting_ordered_set import EmittingOrderedSet
 from .emitting_weak_key_default_dict import EmittingWeakKeyDefaultDict
diff --git a/source_py2/python_toolbox/nifty_collections/frozen_dict.py b/source_py2/python_toolbox/nifty_collections/frozen_dict.py
@@ -0,0 +1,41 @@
+# Copyright 2009-2013 Ram Rachum.
+# This program is distributed under the MIT license.
+
+import collections
+import operator
+
+
+class FrozenDict(collections.Mapping):
+    '''
+    An immutable `dict`.
+    
+    A `dict` that can't be changed. The advantage of this over `dict` is mainly
+    that it's hashable, and thus can be used as a key in dicts and sets.
+    
+    In other words, `FrozenDict` is to `dict` what `frozenset` is to `set`.
+    '''
+    
+    _hash = None # Overridden by instance when calculating hash.
+
+    def __init__(self, *args, **kwargs):
+        self._dict = dict(*args, **kwargs)
+
+    __getitem__ = lambda self, key: self._dict[key]
+    __len__ = lambda self: len(self._dict)
+    __iter__ = lambda self: iter(self._dict)
+
+    def copy(self, *args, **kwargs):
+        base_dict = self._dict.copy()
+        base_dict.update(*args, **kwargs)
+        return type(self)(base_dict)
+    
+    def __hash__(self):
+        if self._hash is None:
+            self._hash = reduce(operator.xor,
+                                map(hash, self.iteritems()),
+                                0) ^ len(self)
+
+        return self._hash
+    
+    __repr__ = lambda self: '<FrozenDict %s>' % repr(self._dict)
+    
diff --git a/source_py2/test_python_toolbox/test_nifty_collections/test_lazy_tuple/test_frozen_dict.py b/source_py2/test_python_toolbox/test_nifty_collections/test_lazy_tuple/test_frozen_dict.py
@@ -0,0 +1,37 @@
+# Copyright 2009-2013 Ram Rachum.
+# This program is distributed under the MIT license.
+
+'''Testing module for `python_toolbox.nifty_collections.LazyTuple`.'''
+
+import uuid
+import itertools
+import collections
+
+from python_toolbox import cute_iter_tools
+from python_toolbox import sequence_tools
+from python_toolbox import cute_testing
+
+
+from python_toolbox.nifty_collections import FrozenDict
+
+
+def test():
+    frozen_dict = FrozenDict({'1': 'a', '2': 'b', '3': 'c',})
+    assert len(frozen_dict) == 3
+    assert set(frozen_dict) == set(frozen_dict.keys()) == \
+                                set(frozen_dict.iterkeys()) == set('123')
+    assert set(frozen_dict.values()) == \
+                                    set(frozen_dict.itervalues()) == set('abc')
+    assert set(frozen_dict.items()) == \
+          set(frozen_dict.iteritems()) == {('1', 'a'), ('2', 'b'), ('3', 'c'),}
+    assert frozen_dict['1'] == 'a'
+    with cute_testing.RaiseAssertor(exception_type=LookupError):
+        frozen_dict['missing value']
+    assert {frozen_dict, frozen_dict} == {frozen_dict}
+    assert {frozen_dict: frozen_dict} == {frozen_dict: frozen_dict}
+    assert isinstance(hash(frozen_dict), int)
+    
+    assert frozen_dict.copy({'meow': 'frrr'}) == \
+           frozen_dict.copy(meow='frrr') == \
+           FrozenDict({'1': 'a', '2': 'b', '3': 'c', 'meow': 'frrr',})
+    
