From e0b5daaee714f2f4bd97a869d0b113e0f7bec168 Mon Sep 17 00:00:00 2001
From: galipremsagar <sagarprem75@gmail.com>
Date: Thu, 7 Jan 2021 07:47:35 -0800
Subject: [PATCH] add informative error message for sep

---
 python/cudf/cudf/io/csv.py         |  7 ++++++-
 python/cudf/cudf/tests/test_csv.py | 24 ++++++++++++++++++++++--
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/python/cudf/cudf/io/csv.py b/python/cudf/cudf/io/csv.py
index 2766e0d79d0..fd040181ca8 100644
--- a/python/cudf/cudf/io/csv.py
+++ b/python/cudf/cudf/io/csv.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2018-2020, NVIDIA CORPORATION.
+# Copyright (c) 2018-2021, NVIDIA CORPORATION.
 
 from io import BytesIO, StringIO
 
@@ -119,6 +119,11 @@ def to_csv(
 ):
     """{docstring}"""
 
+    if not isinstance(sep, str):
+        raise TypeError(f'"sep" must be string, not {type(sep).__name__}')
+    elif len(sep) > 1:
+        raise TypeError('"sep" must be a 1-character string')
+
     return_as_string = False
     if path_or_buf is None:
         path_or_buf = StringIO()
diff --git a/python/cudf/cudf/tests/test_csv.py b/python/cudf/cudf/tests/test_csv.py
index 94a5f061383..0ea8b3add4b 100644
--- a/python/cudf/cudf/tests/test_csv.py
+++ b/python/cudf/cudf/tests/test_csv.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2018-2020, NVIDIA CORPORATION.
+# Copyright (c) 2018-2021, NVIDIA CORPORATION.
 
 import csv
 import gzip
@@ -15,7 +15,7 @@
 
 import cudf
 from cudf import read_csv
-from cudf.tests.utils import assert_eq
+from cudf.tests.utils import assert_eq, assert_exceptions_equal
 
 
 def make_numeric_dataframe(nrows, dtype):
@@ -1935,3 +1935,23 @@ def test_na_filter_empty_fields():
         StringIO(buffer), keep_default_na=False, na_values=test_na
     )
     assert_eq(pdf, gdf)
+
+
+def test_csv_sep_error():
+    pdf = pd.DataFrame({"a": [1, 2, 3]})
+    gdf = cudf.DataFrame({"a": [1, 2, 3]})
+    assert_exceptions_equal(
+        lfunc=pdf.to_csv,
+        rfunc=gdf.to_csv,
+        lfunc_args_and_kwargs=([], {"sep": "abc"}),
+        rfunc_args_and_kwargs=([], {"sep": "abc"}),
+        expected_error_message='"sep" must be a 1-character string',
+    )
+
+    assert_exceptions_equal(
+        lfunc=pdf.to_csv,
+        rfunc=gdf.to_csv,
+        lfunc_args_and_kwargs=([], {"sep": 1}),
+        rfunc_args_and_kwargs=([], {"sep": 1}),
+        expected_error_message='"sep" must be string, not int',
+    )