fix name=True bug

Author: topper-123

doc/source/whatsnew/v1.1.2.rst

@@ -26,7 +26,7 @@ Bug fixes
 ~~~~~~~~~
 - Bug in :meth:`DataFrame.eval` with ``object`` dtype column binary operations (:issue:`35794`)
 - Bug in :meth:`DataFrame.apply` with ``result_type="reduce"`` returning with incorrect index (:issue:`35683`)
--
+- Bug in :meth:`DateTimeIndex.format` and :meth:`PeriodIndex.format` with ``name=True`` setting the first item to ``"None"`` where it should bw ``""`` (:issue:`35712`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/core/indexes/datetimelike.py

@@ -354,8 +354,11 @@ def format(
         """
         header = []
         if name:
-            fmt_name = ibase.pprint_thing(self.name, escape_chars=("\t", "\r", "\n"))
-            header.append(fmt_name)
+            header.append(
+                ibase.pprint_thing(self.name, escape_chars=("\t", "\r", "\n"))
+                if self.name is not None
+                else ""
+            )
 
         if formatter is not None:
             return header + list(self.map(formatter))

pandas/core/indexes/range.py

@@ -189,7 +189,7 @@ def _format_data(self, name=None):
 
     def _format_with_header(self, header: List[str], na_rep: str = "NaN") -> List[str]:
         if len(self._range) == 0:
-            return []
+            return header
         first_val_str = str(self._range[0])
         last_val_str = str(self._range[-1])
         max_length = max(len(first_val_str), len(last_val_str))

pandas/tests/indexes/common.py

@@ -683,7 +683,9 @@ def test_format(self):
 
     def test_format_empty(self):
         # GH35712
-        assert self._holder([]).format() == []
+        empty_idx = self._holder([])
+        assert empty_idx.format() == []
+        assert empty_idx.format(name=True) == [""]
 
     def test_hasnans_isnans(self, index):
         # GH 11343, added tests for hasnans / isnans

pandas/tests/indexes/period/test_period.py

@@ -538,7 +538,9 @@ def test_contains_raise_error_if_period_index_is_in_multi_index(self, msg, key):
 
     def test_format_empty(self):
         # GH35712
-        assert self._holder([], freq="A").format() == []
+        empty_idx = self._holder([], freq="A")
+        assert empty_idx.format() == []
+        assert empty_idx.format(name=True) == [""]
 
 
 def test_maybe_convert_timedelta():

pandas/tests/indexes/ranges/test_range.py

@@ -524,4 +524,6 @@ def test_engineless_lookup(self):
 
     def test_format_empty(self):
         # GH35712
-        assert self._holder(0).format() == []
+        empty_idx = self._holder(0)
+        assert empty_idx.format() == []
+        assert empty_idx.format(name=True) == [""]