Throw TypeError around any call in `if hasattr(obj, '__iter__') a…

…nd not isinstance(obj, str):` to deal with a numpy special case (#4382)

This `TypeError` is thrown from the `numpy` source: https://github.com/numpy/numpy/blob/ffcf508951f646c2ae02c2a0583b884f7a9163e8/numpy/core/src/multiarray/arrayobject.c#L1700-L1702

Fixes: #4030

cirq-core/cirq/protocols/json_serialization.py

@@ -442,8 +442,15 @@ def has_serializable_by_keys(obj: Any) -> bool:
     # Handle primitive container types.
     if isinstance(obj, Dict):
         return any(has_serializable_by_keys(elem) for pair in obj.items() for elem in pair)
+
     if hasattr(obj, '__iter__') and not isinstance(obj, str):
-        return any(has_serializable_by_keys(elem) for elem in obj)
+        # Return False on TypeError because some numpy values
+        # (like np.array(1)) have iterable methods
+        # yet return a TypeError when there is an attempt to iterate over them
+        try:
+            return any(has_serializable_by_keys(elem) for elem in obj)
+        except TypeError:
+            return False
     return False
 
 

cirq-core/cirq/protocols/json_serialization_test.py

@@ -796,3 +796,12 @@ def custom_resolver(name):
             return QuantumVolumeParams
 
     assert_json_roundtrip_works(qvp, resolvers=[custom_resolver] + cirq.DEFAULT_RESOLVERS)
+
+
+def test_numpy_values():
+    assert (
+        cirq.to_json({'value': np.array(1)})
+        == """{
+  "value": 1
+}"""
+    )