Fix for getting a non-existing key from a dict (#77)

observ/observables.py

@@ -240,7 +240,10 @@ def read_key_trap(method, obj_cls):
     def inner(self, *args, **kwargs):
         if Dep.stack:
             key = args[0]
-            proxy_db.attrs(self)["keydep"][key].depend()
+            keydeps = proxy_db.attrs(self)["keydep"]
+            if key not in keydeps:
+                keydeps[key] = Dep()
+            keydeps[key].depend()
         value = fn(self.target, *args, **kwargs)
         if self.shallow:
             return value
@@ -282,7 +285,7 @@ def inner(self, *args, **kwargs):
 
 def write_key_trap(method, obj_cls):
     fn = getattr(obj_cls, method)
-    getitem_fn = getattr(obj_cls, "__getitem__")
+    getitem_fn = getattr(obj_cls, "get")
 
     @wraps(fn)
     def inner(self, *args, **kwargs):

tests/test_usage.py

@@ -625,3 +625,63 @@ def _callback():
     # write to a class attribute
     a[2].foo = 10
     assert called == 2  # class instances are NOT reactive
+
+
+def test_watch_get_non_existing():
+    a = reactive({})
+
+    def result():
+        return a.get("foo", False)
+
+    watcher = watch(result, None, sync=True)
+
+    assert watcher.value is False
+
+    a["foo"] = True
+
+    assert watcher.value is True
+
+
+def test_watch_get_non_existing_dict():
+    a = reactive(dict())
+
+    def result():
+        return "foo" in a
+
+    watcher = watch(result, None, sync=True)
+
+    assert watcher.value is False
+
+    a["foo"] = "bar"
+
+    assert watcher.value is True
+
+
+def test_watch_get_non_existing_set():
+    a = reactive(set())
+
+    def result():
+        return "foo" in a
+
+    watcher = watch(result, None, sync=True)
+
+    assert watcher.value is False
+
+    a.add("foo")
+
+    assert watcher.value is True
+
+
+def test_watch_get_non_existing_list():
+    a = reactive(list())
+
+    def result():
+        return "foo" in a
+
+    watcher = watch(result, None, sync=True)
+
+    assert watcher.value is False
+
+    a.append("foo")
+
+    assert watcher.value is True