Backport PR #31017: REG: restore format_type attr (#31206)

Co-authored-by: jbrockmendel <jbrockmendel@gmail.com>

Author: 2 people

pandas/io/pytables.py

@@ -2474,6 +2474,7 @@ class Fixed:
         """
 
     pandas_kind: str
+    format_type: str = "fixed"  # GH#30962 needed by dask
     obj_type: Type[Union[DataFrame, Series]]
     ndim: int
     encoding: str
@@ -3132,6 +3133,7 @@ class Table(Fixed):
         """
 
     pandas_kind = "wide_table"
+    format_type: str = "table"  # GH#30962 needed by dask
     table_type: str
     levels = 1
     is_table = True

pandas/tests/io/pytables/test_store.py

@@ -64,6 +64,16 @@
 
 @pytest.mark.single
 class TestHDFStore:
+    def test_format_type(self, setup_path):
+        df = pd.DataFrame({"A": [1, 2]})
+        with ensure_clean_path(setup_path) as path:
+            with HDFStore(path) as store:
+                store.put("a", df, format="fixed")
+                store.put("b", df, format="table")
+
+                assert store.get_storer("a").format_type == "fixed"
+                assert store.get_storer("b").format_type == "table"
+
     def test_format_kwarg_in_constructor(self, setup_path):
         # GH 13291