BUG: preserve timezone info when writing empty tz-aware frame to HDF5 (pandas-dev#37069)

Author: arw2019

doc/source/whatsnew/v1.2.0.rst

@@ -433,6 +433,7 @@ I/O
 - Bug in :meth:`to_json` with ``lines=True`` and ``orient='records'`` the last line of the record is not appended with 'new line character' (:issue:`36888`)
 - Bug in :meth:`read_parquet` with fixed offset timezones. String representation of timezones was not recognized (:issue:`35997`, :issue:`36004`)
 - Bug in output rendering of complex numbers showing too many trailing zeros (:issue:`36799`)
+- Bug in :class:`HDFStore` threw a ``TypeError`` when exporting an empty :class:`DataFrame` with ``datetime64[ns, tz]`` dtypes with a fixed HDF5 store (:issue:`20594`)
 
 Plotting
 ^^^^^^^^

pandas/io/pytables.py

@@ -3027,8 +3027,6 @@ def write_array(self, key: str, value: ArrayLike, items: Optional[Index] = None)
             vlarr = self._handle.create_vlarray(self.group, key, _tables().ObjectAtom())
             vlarr.append(value)
 
-        elif empty_array:
-            self.write_array_empty(key, value)
         elif is_datetime64_dtype(value.dtype):
             self._handle.create_array(self.group, key, value.view("i8"))
             getattr(self.group, key)._v_attrs.value_type = "datetime64"
@@ -3043,6 +3041,8 @@ def write_array(self, key: str, value: ArrayLike, items: Optional[Index] = None)
         elif is_timedelta64_dtype(value.dtype):
             self._handle.create_array(self.group, key, value.view("i8"))
             getattr(self.group, key)._v_attrs.value_type = "timedelta64"
+        elif empty_array:
+            self.write_array_empty(key, value)
         else:
             self._handle.create_array(self.group, key, value)
 

pandas/tests/io/pytables/test_timezones.py

@@ -268,7 +268,7 @@ def test_tseries_select_index_column(setup_path):
         assert rng.tz == result.dt.tz
 
 
-def test_timezones_fixed(setup_path):
+def test_timezones_fixed_format_frame_non_empty(setup_path):
     with ensure_clean_store(setup_path) as store:
 
         # index
@@ -296,6 +296,16 @@ def test_timezones_fixed(setup_path):
         tm.assert_frame_equal(result, df)
 
 
+@pytest.mark.parametrize("dtype", ["datetime64[ns, UTC]", "datetime64[ns, US/Eastern]"])
+def test_timezones_fixed_format_frame_empty(setup_path, dtype):
+    with ensure_clean_store(setup_path) as store:
+        s = Series(dtype=dtype)
+        df = DataFrame({"A": s})
+        store["df"] = df
+        result = store["df"]
+        tm.assert_frame_equal(result, df)
+
+
 def test_fixed_offset_tz(setup_path):
     rng = date_range("1/1/2000 00:00:00-07:00", "1/30/2000 00:00:00-07:00")
     frame = DataFrame(np.random.randn(len(rng), 4), index=rng)