Series.__repr__ with MultiIndex with level name 0

doc/source/whatsnew/v2.2.0.rst

@@ -389,6 +389,8 @@ Styler
 Other
 ^^^^^
 - Bug in :func:`cut` incorrectly allowing cutting of timezone-aware datetimes with timezone-naive bins (:issue:`54964`)
+- Bug in rendering a :class:`Series` with a :class:`MultiIndex` when one of the index level's names is 0 not having that name displayed (:issue:`??`)
+-
 
 .. ***DO NOT USE THIS SECTION***
 

pandas/io/formats/format.py

@@ -298,17 +298,6 @@ def _get_footer(self) -> str:
 
         return str(footer)
 
-    def _get_formatted_index(self) -> tuple[list[str], bool]:
-        index = self.tr_series.index
-
-        if isinstance(index, MultiIndex):
-            have_header = any(name for name in index.names)
-            fmt_index = index.format(names=True)
-        else:
-            have_header = index.name is not None
-            fmt_index = index.format(name=True)
-        return fmt_index, have_header
-
     def _get_formatted_values(self) -> list[str]:
         return format_array(
             self.tr_series._values,
@@ -325,7 +314,8 @@ def to_string(self) -> str:
         if len(series) == 0:
             return f"{type(self.series).__name__}([], {footer})"
 
-        fmt_index, have_header = self._get_formatted_index()
+        have_header = _has_names(series.index)
+        fmt_index = self.tr_series.index.format(name=True)
         fmt_values = self._get_formatted_values()
 
         if self.is_truncated_vertically:

pandas/tests/series/test_repr.py

@@ -21,6 +21,16 @@
 
 
 class TestSeriesRepr:
+    def test_multilevel_name_print_0(self):
+        # None does not get printed, but 0 does
+        # (matching DataFrame and flat index behavior)
+        mi = pd.MultiIndex.from_product([range(2, 3), range(3, 4)], names=[0, None])
+        ser = Series(1.5, index=mi)
+
+        res = repr(ser)
+        expected = "0   \n2  3    1.5\ndtype: float64"
+        assert res == expected
+
     def test_multilevel_name_print(self, lexsorted_two_level_string_multiindex):
         index = lexsorted_two_level_string_multiindex
         ser = Series(range(len(index)), index=index, name="sth")