From 06becedf9d359875b58870928827a22fee51f2e2 Mon Sep 17 00:00:00 2001
From: Matthew Murray <matthewmurray711@gmail.com>
Date: Thu, 26 Sep 2024 11:16:23 -0700
Subject: [PATCH] [DOC] Document environment variable for failing on fallback
 in cudf.pandas

---
 .../cudf/source/developer_guide/cudf_pandas.md | 18 ++++++++++++++++++
 python/cudf/cudf/pandas/fast_slow_proxy.py     |  2 +-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/docs/cudf/source/developer_guide/cudf_pandas.md b/docs/cudf/source/developer_guide/cudf_pandas.md
index a8a6d81d6fb..911a64fa152 100644
--- a/docs/cudf/source/developer_guide/cudf_pandas.md
+++ b/docs/cudf/source/developer_guide/cudf_pandas.md
@@ -136,3 +136,21 @@ Arrays are not almost equal to 7 decimals
  ACTUAL: 1.0
  DESIRED: 2.0.
 ```
+
+Setting the environment variable `CUDF_PANDAS_FAIL_ON_FALLBACK` causes `cudf.pandas` to fail when falling back from cuDF to Pandas.
+For example,
+```python
+import cudf.pandas
+cudf.pandas.install()
+import pandas as pd
+import numpy as np
+
+df = pd.DataFrame({
+    'complex_col': [1 + 2j, 3 + 4j, 5 + 6j]
+})
+
+print(df)
+```
+```
+ProxyFallbackError: The operation failed with cuDF, the reason was <class 'NotImplementedError'>: Series with Complex128DType is not supported.
+```
diff --git a/python/cudf/cudf/pandas/fast_slow_proxy.py b/python/cudf/cudf/pandas/fast_slow_proxy.py
index 0c1cda8810b..c364d55e677 100644
--- a/python/cudf/cudf/pandas/fast_slow_proxy.py
+++ b/python/cudf/cudf/pandas/fast_slow_proxy.py
@@ -965,7 +965,7 @@ def _fast_slow_function_call(
     except Exception as err:
         if _env_get_bool("CUDF_PANDAS_FAIL_ON_FALLBACK", False):
             raise ProxyFallbackError(
-                f"The operation failed with cuDF, the reason was {type(err)}: {err}."
+                f"The operation failed with cuDF, the reason was {type(err)}: {err}"
             ) from err
         with nvtx.annotate(
             "EXECUTE_SLOW",