From 14f5454fd235f045b6781d12adec5d586b2422e5 Mon Sep 17 00:00:00 2001
From: Joel Sonoda <jsonoda@mealticket.com>
Date: Tue, 18 Oct 2022 20:21:59 -0600
Subject: [PATCH 1/3] BUG: CSV C engine raises an error on single line CSV with
 no header when passing extra names (#47566)

* Expect the provided number of columns when the names property is set

* Add tests to demonstrate handling of files with a single row with
  fewer columns.
---
 doc/source/whatsnew/v2.0.0.rst                |  1 +
 pandas/_libs/parsers.pyx                      |  3 +++
 .../io/parser/common/test_common_basic.py     | 20 +++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/doc/source/whatsnew/v2.0.0.rst b/doc/source/whatsnew/v2.0.0.rst
index 5e8677e2ae7a6..bde626e7e8ac3 100644
--- a/doc/source/whatsnew/v2.0.0.rst
+++ b/doc/source/whatsnew/v2.0.0.rst
@@ -252,6 +252,7 @@ MultiIndex
 I/O
 ^^^
 - Bug in :func:`read_sas` caused fragmentation of :class:`DataFrame` and raised :class:`.errors.PerformanceWarning` (:issue:`48595`)
+- Bug in :func:`read_csv` for a single-line csv with fewer columns than :parameter:`names` raised :class:`.errors.ParserError` r ``engine="c"`` (:issue:`47566`)
 -
 
 Period
diff --git a/pandas/_libs/parsers.pyx b/pandas/_libs/parsers.pyx
index 51294037f4cd7..b30e0ff8b099e 100644
--- a/pandas/_libs/parsers.pyx
+++ b/pandas/_libs/parsers.pyx
@@ -744,6 +744,8 @@ cdef class TextReader:
         elif self.names is not None:
             # Names passed
             if self.parser.lines < 1:
+                if not self.has_usecols:
+                    self.parser.expected_fields = len(self.names)
                 self._tokenize_rows(1)
 
             header = [self.names]
@@ -756,6 +758,7 @@ cdef class TextReader:
             # Enforce this unless usecols
             if not self.has_usecols:
                 self.parser.expected_fields = max(field_count, len(self.names))
+
         else:
             # No header passed nor to be found in the file
             if self.parser.lines < 1:
diff --git a/pandas/tests/io/parser/common/test_common_basic.py b/pandas/tests/io/parser/common/test_common_basic.py
index 359b059252556..31ef22f5e339c 100644
--- a/pandas/tests/io/parser/common/test_common_basic.py
+++ b/pandas/tests/io/parser/common/test_common_basic.py
@@ -919,6 +919,26 @@ def test_malformed_second_line(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
+@xfail_pyarrow
+def test_short_single_line(all_parsers):
+    parser = all_parsers
+    columns = ["a", "b", "c"]
+    data = "1,2"
+    result = parser.read_csv(StringIO(data), header=None, names=columns)
+    expected = DataFrame({"a": [1], "b": [2], "c": [np.nan]})
+    tm.assert_frame_equal(result, expected)
+
+
+@xfail_pyarrow
+def test_short_multi_line(all_parsers):
+    parser = all_parsers
+    columns = ["a", "b", "c"]
+    data = "1,2\n1,2"
+    result = parser.read_csv(StringIO(data), header=None, names=columns)
+    expected = DataFrame({"a": [1, 1], "b": [2, 2], "c": [np.nan, np.nan]})
+    tm.assert_frame_equal(result, expected)
+
+
 def test_read_table_posargs_deprecation(all_parsers):
     # https://github.com/pandas-dev/pandas/issues/41485
     data = StringIO("a\tb\n1\t2")

From 5a63da00888d1e08097e9e6cbcd6b5ce5abd3d45 Mon Sep 17 00:00:00 2001
From: Joel Sonoda <jsonoda@mealticket.com>
Date: Wed, 19 Oct 2022 07:14:30 -0600
Subject: [PATCH 2/3] bug-47566: fix formatting and typos in whatsnew

---
 doc/source/whatsnew/v2.0.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.0.0.rst b/doc/source/whatsnew/v2.0.0.rst
index bde626e7e8ac3..742b759c6b14f 100644
--- a/doc/source/whatsnew/v2.0.0.rst
+++ b/doc/source/whatsnew/v2.0.0.rst
@@ -252,7 +252,7 @@ MultiIndex
 I/O
 ^^^
 - Bug in :func:`read_sas` caused fragmentation of :class:`DataFrame` and raised :class:`.errors.PerformanceWarning` (:issue:`48595`)
-- Bug in :func:`read_csv` for a single-line csv with fewer columns than :parameter:`names` raised :class:`.errors.ParserError` r ``engine="c"`` (:issue:`47566`)
+- Bug in :func:`read_csv` for a single-line csv with fewer columns than ``names`` raised :class:`.errors.ParserError` with ``engine="c"`` (:issue:`47566`)
 -
 
 Period

From 9ecc4b0655b6bbdc59b35eb8f2c9b8c8381e0248 Mon Sep 17 00:00:00 2001
From: Joel Sonoda <jsonoda@mealticket.com>
Date: Wed, 19 Oct 2022 10:06:24 -0600
Subject: [PATCH 3/3] bug-47566: added the reference to the gh issue number on
 the added tests

---
 pandas/tests/io/parser/common/test_common_basic.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pandas/tests/io/parser/common/test_common_basic.py b/pandas/tests/io/parser/common/test_common_basic.py
index 31ef22f5e339c..52d8abe76ecbc 100644
--- a/pandas/tests/io/parser/common/test_common_basic.py
+++ b/pandas/tests/io/parser/common/test_common_basic.py
@@ -921,6 +921,7 @@ def test_malformed_second_line(all_parsers):
 
 @xfail_pyarrow
 def test_short_single_line(all_parsers):
+    # GH 47566
     parser = all_parsers
     columns = ["a", "b", "c"]
     data = "1,2"
@@ -931,6 +932,7 @@ def test_short_single_line(all_parsers):
 
 @xfail_pyarrow
 def test_short_multi_line(all_parsers):
+    # GH 47566
     parser = all_parsers
     columns = ["a", "b", "c"]
     data = "1,2\n1,2"