adding immutabledict

Author: crazyeng

wolframclient/deserializers/wxf/wxfconsumer.py

@@ -8,6 +8,7 @@
 from wolframclient.serializers.wxfencoder import constants
 from wolframclient.serializers.wxfencoder.utils import array_to_list
 from wolframclient.utils.api import numpy
+from wolframclient.utils.datastructures import immutabledict
 
 __all__ = ["WXFConsumer", "WXFConsumerNumpy"]
 
@@ -112,7 +113,7 @@ def build_function(self, head, arg_list, **kwargs):
         """
         return WLFunction(head, *arg_list)
 
-    def consume_association(self, current_token, tokens, dict_class=dict, **kwargs):
+    def consume_association(self, current_token, tokens, dict_class=immutabledict, **kwargs):
         """Consume a :class:`~wolframclient.deserializers.wxf.wxfparser.WXFToken` of type *association*.
 
         By default, return a :class:`dict` made from the rules.

wolframclient/utils/datastructures.py

@@ -10,6 +10,50 @@ def __repr__(self):
         return dict.__repr__(self)
 
 
+def _fail(self, *args, **opts):
+    raise TypeError("{0} does not support item assignment".format(self.__class__.__name__))
+
+
+class immutabledict(dict):
+    """
+    hashable dict implementation, suitable for use as a key into
+    other dicts.
+
+        >>> h1 = immutabledict({"apples": 1, "bananas":2})
+        >>> h2 = immutabledict({"bananas": 3, "mangoes": 5})
+        >>> h1+h2
+        immutabledict(apples=1, bananas=3, mangoes=5)
+        >>> d1 = {}
+        >>> d1[h1] = "salad"
+        >>> d1[h1]
+        'salad'
+        >>> d1[h2]
+        Traceback (most recent call last):
+        ...
+        KeyError: immutabledict(bananas=3, mangoes=5)
+
+    based on answers from
+       http://stackoverflow.com/questions/1151658/python-hashable-dicts
+
+    """
+
+    def __hash__(self):
+        return hash(tuple(self.items()))
+
+    __setitem__ = _fail
+    __delitem__ = _fail
+    clear = _fail
+    pop = _fail
+    popitem = _fail
+    setdefault = _fail
+    update = _fail
+
+    def __add__(self, right):
+        result = hashdict(self)
+        dict.update(result, right)
+        return result
+
+
 class Settings(dict):
     """
     Dictionary subclass enabling attribute lookup/assignment of keys/values.