1 files changed, 4 insertions, 1 deletions
diff --git a/ch1p/state.py b/ch1p/state.py
index 1ea2373..587b31c 100644
--- a/ch1p/state.py
+++ b/ch1p/state.py
@@ -39,6 +39,9 @@ class State:
     def __setitem__(self, key, value):
         self._data[key] = value
 
+    def __contains__(self, key):
+        return key in self._data
+
     def __delitem__(self, key):
         if key in self._data:
-            del self._data[key]
-\ No newline at end of file
+            del self._data[key]