From fba714b16151cf6aa170659a1f86d67453bf91c4 Mon Sep 17 00:00:00 2001
From: Licht-T <licht-t@outlook.jp>
Date: Fri, 5 Jan 2018 14:03:53 +0900
Subject: [PATCH 1/2] TST: Add to_csv test for writing the single column CSV

---
 pandas/tests/io/formats/test_to_csv.py | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/pandas/tests/io/formats/test_to_csv.py b/pandas/tests/io/formats/test_to_csv.py
index e12a7196dce6b..52479d21fe082 100644
--- a/pandas/tests/io/formats/test_to_csv.py
+++ b/pandas/tests/io/formats/test_to_csv.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import sys
 import numpy as np
 import pandas as pd
 import pytest
@@ -9,6 +10,30 @@
 
 class TestToCSV(object):
 
+    @pytest.mark.xfail((3, 6, 5) > sys.version_info >= (3, 5),
+                       reason='Python csv library bug')
+    def test_to_csv_with_single_column(self):
+        # GH18676
+        df1 = DataFrame([None, 1])
+        expected1 = """\
+""
+1.0
+"""
+        with tm.ensure_clean('test.csv') as path:
+            df1.to_csv(path, header=None, index=None)
+            with open(path, 'r') as f:
+                assert f.read() == expected1
+
+        df2 = DataFrame([1, None])
+        expected2 = """\
+1.0
+""
+"""
+        with tm.ensure_clean('test.csv') as path:
+            df2.to_csv(path, header=None, index=None)
+            with open(path, 'r') as f:
+                assert f.read() == expected2
+
     def test_to_csv_defualt_encoding(self):
         # GH17097
         df = DataFrame({'col': [u"AAAAA", u"ÄÄÄÄÄ", u"ßßßßß", u"聞聞聞聞聞"]})

From c8dd8135805a9a64eb574d443b13730841148866 Mon Sep 17 00:00:00 2001
From: gfyoung <gfyoung17@gmail.com>
Date: Sat, 10 Feb 2018 23:38:31 -0500
Subject: [PATCH 2/2] Expand comment on why this xfailed test was added

---
 pandas/tests/io/formats/test_to_csv.py | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/io/formats/test_to_csv.py b/pandas/tests/io/formats/test_to_csv.py
index 52479d21fe082..dfa3751bff57a 100644
--- a/pandas/tests/io/formats/test_to_csv.py
+++ b/pandas/tests/io/formats/test_to_csv.py
@@ -11,9 +11,16 @@
 class TestToCSV(object):
 
     @pytest.mark.xfail((3, 6, 5) > sys.version_info >= (3, 5),
-                       reason='Python csv library bug')
+                       reason=("Python csv library bug "
+                               "(see https://bugs.python.org/issue32255)"))
     def test_to_csv_with_single_column(self):
-        # GH18676
+        # see gh-18676, https://bugs.python.org/issue32255
+        #
+        # Python's CSV library adds an extraneous '""'
+        # before the newline when the NaN-value is in
+        # the first row. Otherwise, only the newline
+        # character is added. This behavior is inconsistent
+        # and was patched in https://bugs.python.org/pull_request4672.
         df1 = DataFrame([None, 1])
         expected1 = """\
 ""