From 9196f8d545d1118f1233c1b45e7b740cb95c370c Mon Sep 17 00:00:00 2001
From: Marco Edward Gorelli <33491632+MarcoGorelli@users.noreply.github.com>
Date: Sat, 19 Nov 2022 09:36:58 +0000
Subject: [PATCH] Backport PR STYLE enable pylint: method-cache-max-size-none
 (#49784)

Co-authored-by: Natalia Mokeeva <91160475+natmokval@users.noreply.github.com>
---
 doc/source/whatsnew/v1.5.2.rst           |  2 +-
 pandas/io/formats/excel.py               | 10 +++++++++-
 pandas/tests/io/formats/test_to_excel.py | 10 +++++-----
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/doc/source/whatsnew/v1.5.2.rst b/doc/source/whatsnew/v1.5.2.rst
index c1fde3d13ef74..64f57986cc3e4 100644
--- a/doc/source/whatsnew/v1.5.2.rst
+++ b/doc/source/whatsnew/v1.5.2.rst
@@ -28,7 +28,7 @@ Fixed regressions
 Bug fixes
 ~~~~~~~~~
 - Bug in the Copy-on-Write implementation losing track of views in certain chained indexing cases (:issue:`48996`)
--
+- Fixed memory leak in :meth:`.Styler.to_excel` (:issue:`49751`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_152.other:
diff --git a/pandas/io/formats/excel.py b/pandas/io/formats/excel.py
index ce7f663dd5703..19b766fd70675 100644
--- a/pandas/io/formats/excel.py
+++ b/pandas/io/formats/excel.py
@@ -170,10 +170,13 @@ def __init__(self, inherited: str | None = None) -> None:
             self.inherited = self.compute_css(inherited)
         else:
             self.inherited = None
+        # We should avoid lru_cache on the __call__ method.
+        # Otherwise once the method __call__ has been called
+        # garbage collection no longer deletes the instance.
+        self._call_cached = lru_cache(maxsize=None)(self._call_uncached)
 
     compute_css = CSSResolver()
 
-    @lru_cache(maxsize=None)
     def __call__(
         self, declarations: str | frozenset[tuple[str, str]]
     ) -> dict[str, dict[str, str]]:
@@ -193,6 +196,11 @@ def __call__(
             A style as interpreted by ExcelWriter when found in
             ExcelCell.style.
         """
+        return self._call_cached(declarations)
+
+    def _call_uncached(
+        self, declarations: str | frozenset[tuple[str, str]]
+    ) -> dict[str, dict[str, str]]:
         properties = self.compute_css(declarations, self.inherited)
         return self.build_xlstyle(properties)
 
diff --git a/pandas/tests/io/formats/test_to_excel.py b/pandas/tests/io/formats/test_to_excel.py
index 7481baaee94f6..2a0f9f59972ef 100644
--- a/pandas/tests/io/formats/test_to_excel.py
+++ b/pandas/tests/io/formats/test_to_excel.py
@@ -357,7 +357,7 @@ def test_css_excel_cell_precedence(styles, expected):
     """It applies favors latter declarations over former declarations"""
     # See GH 47371
     converter = CSSToExcelConverter()
-    converter.__call__.cache_clear()
+    converter._call_cached.cache_clear()
     css_styles = {(0, 0): styles}
     cell = CssExcelCell(
         row=0,
@@ -369,7 +369,7 @@ def test_css_excel_cell_precedence(styles, expected):
         css_col=0,
         css_converter=converter,
     )
-    converter.__call__.cache_clear()
+    converter._call_cached.cache_clear()
 
     assert cell.style == converter(expected)
 
@@ -410,7 +410,7 @@ def test_css_excel_cell_cache(styles, cache_hits, cache_misses):
     """It caches unique cell styles"""
     # See GH 47371
     converter = CSSToExcelConverter()
-    converter.__call__.cache_clear()
+    converter._call_cached.cache_clear()
 
     css_styles = {(0, i): _style for i, _style in enumerate(styles)}
     for css_row, css_col in css_styles:
@@ -424,8 +424,8 @@ def test_css_excel_cell_cache(styles, cache_hits, cache_misses):
             css_col=css_col,
             css_converter=converter,
         )
-    cache_info = converter.__call__.cache_info()
-    converter.__call__.cache_clear()
+    cache_info = converter._call_cached.cache_info()
+    converter._call_cached.cache_clear()
 
     assert cache_info.hits == cache_hits
     assert cache_info.misses == cache_misses