Minor optimizations and test for #150

Author: Cito

src/graphql/language/ast.py

@@ -255,12 +255,18 @@ def __eq__(self, other: Any) -> bool:
         )
 
     def __hash__(self) -> int:
-        if getattr(self, "_hash", None) is None:
-            self._hash = hash(tuple(getattr(self, key) for key in self.keys))
-        return self._hash
-
-    def __setattr__(self, key, value):
-        object.__setattr__(self, "_hash", None)
+        """Get a cached hash value for the node."""
+        # Caching the hash values improves the performance of AST validators
+        hashed = getattr(self, "_hash", None)
+        if hashed is None:
+            hashed = hash(tuple(getattr(self, key) for key in self.keys))
+            self._hash = hashed
+        return hashed
+
+    def __setattr__(self, key: str, value: Any) -> None:
+        # reset cashed hash value if attributes are changed
+        if hasattr(self, "_hash") and key in self.keys:
+            del self._hash
         super().__setattr__(key, value)
 
     def __copy__(self) -> "Node":

tests/language/test_ast.py

@@ -180,14 +180,27 @@ def can_hash():
         assert node3 != node
         assert hash(node3) != hash(node)
 
+    def caches_are_hashed():
+        node = SampleTestNode(alpha=1)
+        assert not hasattr(node, "_hash")
+        hash1 = hash(node)
+        assert hasattr(node, "_hash")
+        assert hash1 == getattr(node, "_hash")
+        node.alpha = 2
+        assert not hasattr(node, "_hash")
+        hash2 = hash(node)
+        assert hash2 != hash1
+        assert hasattr(node, "_hash")
+        assert hash2 == getattr(node, "_hash")
+
     def can_create_weak_reference():
         node = SampleTestNode(alpha=1, beta=2)
         ref = weakref.ref(node)
         assert ref() is node
 
     def can_create_custom_attribute():
         node = SampleTestNode(alpha=1, beta=2)
-        node.gamma = 3  # type: ignore
+        node.gamma = 3
         assert node.gamma == 3  # type: ignore
 
     def can_create_shallow_copy():