Backport PR pandas-dev#35440: BUG: CategoricalIndex.format

Author: topper-123

doc/source/whatsnew/v1.1.1.rst

@@ -26,6 +26,13 @@ Fixed regressions
 Bug fixes
 ~~~~~~~~~
 
+
+Categorical
+^^^^^^^^^^^
+
+- Bug in :meth:`CategoricalIndex.format` where, when stringified scalars had different lengths, the shorter string would be right-filled with spaces, so it had the same length as the longest string (:issue:`35439`)
+
+
 **Datetimelike**
 
 -

pandas/core/indexes/category.py

@@ -20,7 +20,7 @@
     pandas_dtype,
 )
 from pandas.core.dtypes.dtypes import CategoricalDtype
-from pandas.core.dtypes.missing import is_valid_nat_for_dtype, isna
+from pandas.core.dtypes.missing import is_valid_nat_for_dtype, isna, notna
 
 from pandas.core import accessor
 from pandas.core.algorithms import take_1d
@@ -348,12 +348,12 @@ def _format_attrs(self):
         return attrs
 
     def _format_with_header(self, header, na_rep="NaN") -> List[str]:
-        from pandas.io.formats.format import format_array
+        from pandas.io.formats.printing import pprint_thing
 
-        formatted_values = format_array(
-            self._values, formatter=None, na_rep=na_rep, justify="left"
-        )
-        result = ibase.trim_front(formatted_values)
+        result = [
+            pprint_thing(x, escape_chars=("\t", "\r", "\n")) if notna(x) else na_rep
+            for x in self._values
+        ]
         return header + result
 
     # --------------------------------------------------------------------

pandas/core/indexes/range.py

@@ -1,7 +1,7 @@
 from datetime import timedelta
 import operator
 from sys import getsizeof
-from typing import Any, List, Optional
+from typing import Any, Optional
 import warnings
 
 import numpy as np
@@ -33,8 +33,6 @@
 from pandas.core.indexes.numeric import Int64Index
 from pandas.core.ops.common import unpack_zerodim_and_defer
 
-from pandas.io.formats.printing import pprint_thing
-
 _empty_range = range(0)
 
 
@@ -197,9 +195,6 @@ def _format_data(self, name=None):
         # we are formatting thru the attributes
         return None
 
-    def _format_with_header(self, header, na_rep="NaN") -> List[str]:
-        return header + [pprint_thing(x) for x in self._range]
-
     # --------------------------------------------------------------------
     _deprecation_message = (
         "RangeIndex.{} is deprecated and will be "

pandas/tests/indexes/categorical/test_category.py

@@ -478,3 +478,9 @@ def test_reindex_base(self):
     def test_map_str(self):
         # See test_map.py
         pass
+
+    def test_format_different_scalar_lengths(self):
+        # GH35439
+        idx = CategoricalIndex(["aaaaaaaaa", "b"])
+        expected = ["aaaaaaaaa", "b"]
+        assert idx.format() == expected

pandas/tests/indexes/common.py

@@ -642,6 +642,12 @@ def test_equals_op(self):
             tm.assert_numpy_array_equal(index_a == item, expected3)
             tm.assert_series_equal(series_a == item, Series(expected3))
 
+    def test_format(self):
+        # GH35439
+        idx = self.create_index()
+        expected = [str(x) for x in idx]
+        assert idx.format() == expected
+
     def test_hasnans_isnans(self, index):
         # GH 11343, added tests for hasnans / isnans
         if isinstance(index, MultiIndex):

pandas/tests/indexes/datetimes/test_datetimelike.py

@@ -20,6 +20,12 @@ def index(self, request):
     def create_index(self) -> DatetimeIndex:
         return date_range("20130101", periods=5)
 
+    def test_format(self):
+        # GH35439
+        idx = self.create_index()
+        expected = [f"{x:%Y-%m-%d}" for x in idx]
+        assert idx.format() == expected
+
     def test_shift(self):
         pass  # handled in test_ops
 

pandas/tests/indexes/test_base.py

@@ -1171,8 +1171,11 @@ def test_summary_bug(self):
         assert "~:{range}:0" in result
         assert "{other}%s" in result
 
-    def test_format(self, index):
-        self._check_method_works(Index.format, index)
+    def test_format_different_scalar_lengths(self):
+        # GH35439
+        idx = Index(["aaaaaaaaa", "b"])
+        expected = ["aaaaaaaaa", "b"]
+        assert idx.format() == expected
 
     def test_format_bug(self):
         # GH 14626

pandas/tests/indexes/test_numeric.py

@@ -21,6 +21,13 @@ def test_can_hold_identifiers(self):
         key = idx[0]
         assert idx._can_hold_identifiers_and_holds_name(key) is False
 
+    def test_format(self):
+        # GH35439
+        idx = self.create_index()
+        max_width = max(len(str(x)) for x in idx)
+        expected = [str(x).ljust(max_width) for x in idx]
+        assert idx.format() == expected
+
     def test_numeric_compat(self):
         pass  # override Base method
 

pandas/tests/io/formats/test_format.py

@@ -2141,6 +2141,15 @@ def test_dict_entries(self):
         assert "'a': 1" in val
         assert "'b': 2" in val
 
+    def test_categorical_columns(self):
+        # GH35439
+        data = [[4, 2], [3, 2], [4, 3]]
+        cols = ["aaaaaaaaa", "b"]
+        df = pd.DataFrame(data, columns=cols)
+        df_cat_cols = pd.DataFrame(data, columns=pd.CategoricalIndex(cols))
+
+        assert df.to_string() == df_cat_cols.to_string()
+
     def test_period(self):
         # GH 12615
         df = pd.DataFrame(