BUG: fix html float display (#59930)

* fix html display float/strings

* add test under io, update whatsnew

* fix linting

* changes to fix floats only

* Revert "fix linting"

This reverts commit 1061442.

* test script for float format

* remove nbsp implementation, keep floats

* Trigger CI

* implement changes post review

* lint check

* update test_formats.py

* rfc test_format.py

* update test cases

Author: saldanhad

doc/source/whatsnew/v3.0.0.rst

@@ -620,6 +620,7 @@ I/O
 ^^^
 - Bug in :class:`DataFrame` and :class:`Series` ``repr`` of :py:class:`collections.abc.Mapping`` elements. (:issue:`57915`)
 - Bug in :meth:`.DataFrame.to_json` when ``"index"`` was a value in the :attr:`DataFrame.column` and :attr:`Index.name` was ``None``. Now, this will fail with a ``ValueError`` (:issue:`58925`)
+- Bug in :meth:`DataFrame._repr_html_` which ignored the ``"display.float_format"`` option (:issue:`59876`)
 - Bug in :meth:`DataFrame.from_records` where ``columns`` parameter with numpy structured array was not reordering and filtering out the columns (:issue:`59717`)
 - Bug in :meth:`DataFrame.to_dict` raises unnecessary ``UserWarning`` when columns are not unique and ``orient='tight'``. (:issue:`58281`)
 - Bug in :meth:`DataFrame.to_excel` when writing empty :class:`DataFrame` with :class:`MultiIndex` on both axes (:issue:`57696`)

pandas/core/frame.py

@@ -1192,14 +1192,15 @@ def _repr_html_(self) -> str | None:
             min_rows = get_option("display.min_rows")
             max_cols = get_option("display.max_columns")
             show_dimensions = get_option("display.show_dimensions")
+            show_floats = get_option("display.float_format")
 
             formatter = fmt.DataFrameFormatter(
                 self,
                 columns=None,
                 col_space=None,
                 na_rep="NaN",
                 formatters=None,
-                float_format=None,
+                float_format=show_floats,
                 sparsify=None,
                 justify=None,
                 index_names=True,

pandas/tests/io/formats/test_format.py

@@ -368,6 +368,23 @@ def test_repr_min_rows(self):
             assert ".." not in repr(df)
             assert ".." not in df._repr_html_()
 
+    @pytest.mark.parametrize(
+        "data, format_option, expected_values",
+        [
+            (12345.6789, "{:12.3f}", "12345.679"),
+            (None, "{:.3f}", "None"),
+            ("", "{:.2f}", ""),
+            (112345.6789, "{:6.3f}", "112345.679"),
+        ],
+    )
+    def test_repr_float_formatting_html_output(
+        self, data, format_option, expected_values
+    ):
+        with option_context("display.float_format", format_option.format):
+            df = DataFrame({"A": [data]})
+            html_output = df._repr_html_()
+            assert expected_values in html_output
+
     def test_str_max_colwidth(self):
         # GH 7856
         df = DataFrame(