Make Slice a proper LazyValueWrapper

jedi/inference/base_value.py

@@ -19,7 +19,7 @@ from jedi.inference.utils import safe_property
 from jedi.inference.cache import inference_state_as_method_param_cache
 from jedi.cache import memoize_method
 
-_sentinel = object()
+sentinel = object()
 
 
 class HelperValueMixin(object):
@@ -205,8 +205,8 @@ class Value(HelperValueMixin, BaseValue):
             return clean_scope_docstring(self.tree_node)
         return None
 
-    def get_safe_value(self, default=_sentinel):
-        if default is _sentinel:
+    def get_safe_value(self, default=sentinel):
+        if default is sentinel:
             raise ValueError("There exists no safe value for value %s" % self)
         return default
 
@@ -360,8 +360,6 @@ class ContextualizedName(ContextualizedNode):
 
 
 def _getitem(value, index_values, contextualized_node):
-    from jedi.inference.value.iterable import Slice
-
     # The actual getitem call.
     simple_getitem = getattr(value, 'py__simple_getitem__', None)
 
@@ -369,17 +367,8 @@ def _getitem(value, index_values, contextualized_node):
     unused_values = set()
     for index_value in index_values:
         if simple_getitem is not None:
-            index = index_value
-            if isinstance(index_value, Slice):
-                index = index.obj
-
-            try:
-                method = index.get_safe_value
-            except AttributeError:
-                pass
-            else:
-                index = method(default=None)
 
+            index = index_value.get_safe_value(default=None)
             if type(index) in (float, int, str, unicode, slice, bytes):
                 try:
                     result |= simple_getitem(index)

jedi/inference/value/iterable.py

@@ -37,7 +37,8 @@ from jedi.inference.utils import safe_property, to_list
 from jedi.inference.cache import inference_state_method_cache
 from jedi.inference.filters import LazyAttributeOverwrite, publish_method
 from jedi.inference.base_value import ValueSet, Value, NO_VALUES, \
-    ContextualizedNode, iterate_values, HelperValueMixin, _sentinel
+    ContextualizedNode, iterate_values, HelperValueMixin, sentinel, \
+    LazyValueWrapper
 from jedi.parser_utils import get_sync_comp_fors
 from jedi.inference.context import CompForContext
 
@@ -54,8 +55,8 @@ class IterableMixin(object):
     # typeshed.
     if sys.version_info[0] == 2:
         # Python 2...........
-        def get_safe_value(self, default=_sentinel):
-            if default is _sentinel:
+        def get_safe_value(self, default=sentinel):
+            if default is sentinel:
                 raise ValueError("There exists no safe value for value %s" % self)
             return default
     else:
@@ -771,23 +772,21 @@ class _ArrayInstance(HelperValueMixin):
         return self.py__iter__(contextualized_node)
 
 
-class Slice(object):
+class Slice(LazyValueWrapper):
     def __init__(self, python_context, start, stop, step):
-        self._python_context = python_context
-        self._slice_object = None
+        self.inference_state = python_context.inference_state
+        self._context = python_context
         # All of them are either a Precedence or None.
         self._start = start
         self._stop = stop
         self._step = step
 
-    def __getattr__(self, name):
-        if self._slice_object is None:
-            value = compiled.builtin_from_name(self._python_context.inference_state, 'slice')
-            self._slice_object, = value.execute_with_values()
-        return getattr(self._slice_object, name)
+    def _get_wrapped_value(self):
+        value = compiled.builtin_from_name(self._context.inference_state, 'slice')
+        slice_value, = value.execute_with_values()
+        return slice_value
 
-    @property
-    def obj(self):
+    def get_safe_value(self, default=sentinel):
         """
         Imitate CompiledObject.obj behavior and return a ``builtin.slice()``
         object.
@@ -796,7 +795,7 @@ class Slice(object):
             if element is None:
                 return None
 
-            result = self._python_context.infer_node(element)
+            result = self._context.infer_node(element)
             if len(result) != 1:
                 # For simplicity, we want slices to be clear defined with just
                 # one type.  Otherwise we will return an empty slice object.