BUG: Fix render as column name in to_excel

doc/source/whatsnew/v1.1.0.rst

@@ -794,6 +794,7 @@ I/O
 - Bug in :meth:`~DataFrame.read_feather` was raising an `ArrowIOError` when reading an s3 or http file path (:issue:`29055`)
 - Bug in :meth:`read_parquet` was raising a ``FileNotFoundError`` when passed an s3 directory path. (:issue:`26388`)
 - Bug in :meth:`~DataFrame.to_parquet` was throwing an ``AttributeError`` when writing a partitioned parquet file to s3 (:issue:`27596`)
+- Bug in :meth:`~DataFrame.to_excel` could not handle the column name `render` and was raising an ``KeyError`` (:issue:`34331`)
 
 Plotting
 ^^^^^^^^

pandas/io/formats/excel.py

@@ -16,7 +16,7 @@
 from pandas.core.dtypes.common import is_float, is_scalar
 from pandas.core.dtypes.generic import ABCIndex
 
-from pandas import Index, MultiIndex, PeriodIndex
+from pandas import DataFrame, Index, MultiIndex, PeriodIndex
 import pandas.core.common as com
 
 from pandas.io.common import stringify_path
@@ -385,7 +385,7 @@ def __init__(
     ):
         self.rowcounter = 0
         self.na_rep = na_rep
-        if hasattr(df, "render"):
+        if hasattr(df, "render") and not isinstance(df, DataFrame):
             self.styler = df
             df = df.data
             if style_converter is None:

pandas/tests/io/excel/test_openpyxl.py

@@ -107,10 +107,11 @@ def test_write_append_mode(ext, mode, expected):
             assert wb2.worksheets[index]["A1"].value == cell_value
 
 
-def test_to_excel_with_openpyxl_engine(ext, tmpdir):
+@pytest.mark.parametrize("col", ["B", "render"])
+def test_to_excel_with_openpyxl_engine(ext, tmpdir, col):
     # GH 29854
     df1 = DataFrame({"A": np.linspace(1, 10, 10)})
-    df2 = DataFrame({"B": np.linspace(1, 20, 10)})
+    df2 = DataFrame({col: 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")

pandas/tests/io/excel/test_writers.py

@@ -1201,6 +1201,14 @@ def test_write_lists_dict(self, path):
 
         tm.assert_frame_equal(read, expected)
 
+    def test_render_as_column_name(self, path):
+        # see gh-34331
+        df = DataFrame({"render": [1, 2], "data": [3, 4]})
+        df.to_excel(path, "Sheet1")
+        read = pd.read_excel(path, "Sheet1", index_col=0)
+        expected = df
+        tm.assert_frame_equal(read, expected)
+
     def test_true_and_false_value_options(self, path):
         # see gh-13347
         df = pd.DataFrame([["foo", "bar"]], columns=["col1", "col2"])