fix: histogram metadata not being serialized correctly (#1038)

* fix: histogram metadata not being serialized correctly

Signed-off-by: Henry Schreiner <[email protected]>

* style: pre-commit fixes

---------

Signed-off-by: Henry Schreiner <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: henryiii

src/boost_histogram/serialization/__init__.py

@@ -25,10 +25,7 @@ def to_uhi(h: histogram.Histogram, /) -> dict[str, Any]:
         "axes": [_axis_to_dict(axis) for axis in h.axes],
         "storage": _storage_to_dict(h.storage_type(), h.view(flow=True)),
     }
-    if h.metadata is not None:
-        data["metadata"] = {
-            k: v for k, v in h.metadata.items() if not k.startswith("@")
-        }
+    data["metadata"] = {k: v for k, v in h.__dict__.items() if not k.startswith("@")}
 
     return data
 

src/boost_histogram/tag.py

@@ -20,7 +20,7 @@
 
 def Slicer() -> np.lib._index_tricks_impl.IndexExpression:
     """
-    It is encouraged to use "np.s_" directly instead of this function:
+    It is encouraged to use ``np.s_`` directly instead of this function:
 
         h[{0: np.s_[::bh.rebin(2)]}]   # rebin axis 0 by two
 

tests/test_serialization_uhi.py

@@ -25,7 +25,6 @@ def test_simple_to_dict(storage_type: bh.storage.Storage, expected_type: str) ->
     )
     data = to_uhi(h)
 
-    assert "metadata" not in data
     assert data["axes"][0]["type"] == "regular"
     assert data["axes"][0]["lower"] == 0
     assert data["axes"][0]["upper"] == 1
@@ -61,8 +60,8 @@ def test_mean_to_dict() -> None:
     h = bh.Histogram(
         bh.axis.StrCategory(["one", "two", "three"]),
         storage=bh.storage.Mean(),
-        metadata={"name": "hi"},
     )
+    h.name = "hi"
     data = to_uhi(h)
 
     assert data["metadata"]["name"] == "hi"
@@ -239,9 +238,28 @@ def test_round_trip_clean() -> None:
 
 def test_unserializable_metadata() -> None:
     h = bh.Histogram(
-        bh.axis.Integer(0, 10, metadata={"c": 3, "@d": 4}), metadata={"a": 1, "@b": 2}
+        bh.axis.Integer(0, 10, metadata={"c": 3, "@d": 4}),
     )
+    h.__dict__["a"] = 1
+    h.__dict__["@b"] = 2
     data = to_uhi(h)
 
-    assert data["metadata"] == {"a": 1}
+    assert data["metadata"] == {"a": 1, "_variance_known": True, "metadata": None}
     assert data["axes"][0]["metadata"] == {"c": 3}
+
+
+def test_histogram_metadata() -> None:
+    h = bh.Histogram(bh.axis.Integer(0, 10))
+    h.name = "Hi"
+    h.label = "hi"
+    h.other = 3
+
+    data = to_uhi(h)
+
+    assert data["metadata"] == {
+        "name": "Hi",
+        "label": "hi",
+        "other": 3,
+        "_variance_known": True,
+        "metadata": None,
+    }