Add Underscore class

spacy/tokens/underscore.py

@@ -0,0 +1,38 @@
+class Undercore(object):
+    doc_extensions = {}
+    span_extensions = {}
+    token_extensions = {}
+
+    def __init__(self, obj, start=None, end=None):
+        object.__setattr__(self, '_obj', obj)
+        # Assumption is that for doc values, _start and _end will both be None
+        # Span will set non-None values for _start and _end
+        # Token will have _start be non-None, _end be None
+        # This lets us key everything into the doc.user_data dictionary,
+        # (see _get_key), and lets us use a single Underscore class.
+        object.__setattr__(self, '_doc', obj.doc)
+        object.__setattr__(self, '_start', start)
+        object.__setattr__(self, '_end', start)
+
+    def __getattr__(self, name):
+        if name not in self.__class__.extensions:
+            raise AttributeError(name)
+        default, method, getter, setter = self.__class__.extensions[name]
+        if getter is not None:
+            return getter(self._obj)
+        elif method is not None:
+            return method)
+        else:
+            return self._doc.user_data.get(self._get_key(name), default)
+
+    def __setattr__(self, name, value):
+        if name not in self.__class__.extensions:
+            raise AttributeError(name)
+        default, method, getter, setter = self.__class__.extensions[name]
+        if setter is not None:
+            return setter(self._obj, value)
+        else:
+            self._doc.user_data[self._get_key(name)] = value
+
+    def _get_key(self, name):
+        return ('._.', name, self._start, self._end)