REF: De-special-case _format_with_header (#55491)

* REF: De-special-case _format_with_header

* simplify

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -1387,12 +1387,20 @@ def _format_with_header(self, *, header: list[str_t], na_rep: str_t) -> list[str
 
         values = self._values
 
-        if is_object_dtype(values.dtype) or is_string_dtype(values.dtype):
-            values = np.asarray(values)
+        if (
+            is_object_dtype(values.dtype)
+            or is_string_dtype(values.dtype)
+            or isinstance(self.dtype, (IntervalDtype, CategoricalDtype))
+        ):
             # TODO: why do we need different justify for these cases?
-            result = trim_front(format_array(values, None, justify="all"))
+            justify = "all"
         else:
-            result = trim_front(format_array(values, None, justify="left"))
+            justify = "left"
+        # passing leading_space=False breaks test_format_missing,
+        #  test_index_repr_in_frame_with_nan, but would otherwise make
+        #  trim_front unnecessary
+        formatted = format_array(values, None, justify=justify)
+        result = trim_front(formatted)
         return header + result
 
     def _format_native_types(

pandas/core/indexes/category.py

@@ -21,7 +21,6 @@
 from pandas.core.dtypes.missing import (
     is_valid_na_for_dtype,
     isna,
-    notna,
 )
 
 from pandas.core.arrays.categorical import (
@@ -38,8 +37,6 @@
     inherit_names,
 )
 
-from pandas.io.formats.printing import pprint_thing
-
 if TYPE_CHECKING:
     from collections.abc import Hashable
 
@@ -356,13 +353,6 @@ def _format_attrs(self):
         extra = super()._format_attrs()
         return attrs + extra
 
-    def _format_with_header(self, *, header: list[str], na_rep: str) -> list[str]:
-        result = [
-            pprint_thing(x, escape_chars=("\t", "\r", "\n")) if notna(x) else na_rep
-            for x in self._values
-        ]
-        return header + result
-
     # --------------------------------------------------------------------
 
     @property

pandas/core/indexes/datetimelike.py

@@ -216,6 +216,7 @@ def format(
     def _format_with_header(
         self, *, header: list[str], na_rep: str, date_format: str | None = None
     ) -> list[str]:
+        # TODO: not reached in tests 2023-10-11
         # matches base class except for whitespace padding and date_format
         return header + list(
             self._format_native_types(na_rep=na_rep, date_format=date_format)

pandas/core/indexes/interval.py

@@ -842,13 +842,6 @@ def mid(self) -> Index:
     def length(self) -> Index:
         return Index(self._data.length, copy=False)
 
-    # --------------------------------------------------------------------
-    # Rendering Methods
-
-    def _format_with_header(self, *, header: list[str], na_rep: str) -> list[str]:
-        # matches base class except for whitespace padding
-        return header + list(self._format_native_types(na_rep=na_rep))
-
     # --------------------------------------------------------------------
     # Set Operations