CI: Fix version openpyxl

environment.yml

@@ -78,7 +78,7 @@ dependencies:
   - fastparquet>=0.3.2  # pandas.read_parquet, DataFrame.to_parquet
   - html5lib  # pandas.read_html
   - lxml  # pandas.read_html
-  - openpyxl  # pandas.read_excel, DataFrame.to_excel, pandas.ExcelWriter, pandas.ExcelFile
+  - openpyxl<=3.0.1  # pandas.read_excel, DataFrame.to_excel, pandas.ExcelWriter, pandas.ExcelFile
   - pyarrow>=0.13.1  # pandas.read_parquet, DataFrame.to_parquet, pandas.read_feather, DataFrame.to_feather
   - pyqt>=5.9.2  # pandas.read_clipboard
   - pytables>=3.4.2  # pandas.read_hdf, DataFrame.to_hdf

pandas/tests/io/excel/test_openpyxl.py

@@ -1,5 +1,9 @@
+import os
+
+import numpy as np
 import pytest
 
+import pandas as pd
 from pandas import DataFrame
 import pandas.util.testing as tm
 
@@ -101,3 +105,21 @@ def test_write_append_mode(ext, mode, expected):
 
         for index, cell_value in enumerate(expected):
             assert wb2.worksheets[index]["A1"].value == cell_value
+
+
+@pytest.mark.xfail(openpyxl.__version__ > "3.0.1", reason="broken change in openpyxl")
+def test_to_excel_with_openpyxl_engine(ext, tmpdir):
+    # GH 29854
+    # TODO: Fix this once newer version of openpyxl fixes the bug
+    df1 = DataFrame({"A": np.linspace(1, 10, 10)})
+    df2 = DataFrame({"B": np.linspace(1, 20, 10)})
+    df = pd.concat([df1, df2], axis=1)
+    styled = df.style.applymap(
+        lambda val: "color: %s" % "red" if val < 0 else "black"
+    ).highlight_max()
+
+    filename = tmpdir / "styled.xlsx"
+    styled.to_excel(filename, engine="openpyxl")
+
+    assert filename.exists()
+    os.remove(filename)

requirements-dev.txt

@@ -51,7 +51,7 @@ beautifulsoup4>=4.6.0
 fastparquet>=0.3.2
 html5lib
 lxml
-openpyxl
+openpyxl<=3.0.1
 pyarrow>=0.13.1
 pyqt5>=5.9.2
 tables>=3.4.2