From bd3e37f9140c9fff3924098cd7754cd49015404a Mon Sep 17 00:00:00 2001
From: MeeseeksMachine <39504233+meeseeksmachine@users.noreply.github.com>
Date: Sat, 26 Sep 2020 04:32:17 -0700
Subject: [PATCH] Backport PR #36560: [BUG]: Fix regression in read_table with
 delim_whitespace=True (#36661)

Co-authored-by: patrick <61934744+phofl@users.noreply.github.com>
---
 doc/source/whatsnew/v1.1.3.rst        |  1 +
 pandas/io/parsers.py                  | 10 ++++++++++
 pandas/tests/io/parser/test_common.py | 21 +++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/doc/source/whatsnew/v1.1.3.rst b/doc/source/whatsnew/v1.1.3.rst
index aeb9076617787..eded30ca45025 100644
--- a/doc/source/whatsnew/v1.1.3.rst
+++ b/doc/source/whatsnew/v1.1.3.rst
@@ -40,6 +40,7 @@ Fixed regressions
 - Fixed regression in :meth:`DataFrame.apply` with ``raw=True`` and user-function returning string (:issue:`35940`)
 - Fixed regression when setting empty :class:`DataFrame` column to a :class:`Series` in preserving name of index in frame (:issue:`36527`)
 - Fixed regression in :class:`Period` incorrect value for ordinal over the maximum timestamp (:issue:`36430`)
+- Fixed regression in :func:`read_table` raised ``ValueError`` when ``delim_whitespace`` was set to ``True`` (:issue:`35958`)
 - Fixed regression in :meth:`Series.dt.normalize` when normalizing pre-epoch dates the result was shifted one day (:issue:`36294`)
 
 .. ---------------------------------------------------------------------------
diff --git a/pandas/io/parsers.py b/pandas/io/parsers.py
index d4f346f8c1087..a02b059967e88 100644
--- a/pandas/io/parsers.py
+++ b/pandas/io/parsers.py
@@ -752,6 +752,16 @@ def read_table(
     memory_map=False,
     float_precision=None,
 ):
+    # TODO: validation duplicated in read_csv
+    if delim_whitespace and (delimiter is not None or sep != "\t"):
+        raise ValueError(
+            "Specified a delimiter with both sep and "
+            "delim_whitespace=True; you can only specify one."
+        )
+    if delim_whitespace:
+        # In this case sep is not used so we set it to the read_csv
+        # default to avoid a ValueError
+        sep = ","
     return read_csv(**locals())
 
 
diff --git a/pandas/tests/io/parser/test_common.py b/pandas/tests/io/parser/test_common.py
index 3d5f6ae3a4af9..c6a43d22ca155 100644
--- a/pandas/tests/io/parser/test_common.py
+++ b/pandas/tests/io/parser/test_common.py
@@ -2191,3 +2191,24 @@ def test_read_csv_with_use_inf_as_na(all_parsers):
         result = parser.read_csv(StringIO(data), header=None)
     expected = DataFrame([1.0, np.nan, 3.0])
     tm.assert_frame_equal(result, expected)
+
+
+def test_read_table_delim_whitespace_default_sep(all_parsers):
+    # GH: 35958
+    f = StringIO("a  b  c\n1 -2 -3\n4  5   6")
+    parser = all_parsers
+    result = parser.read_table(f, delim_whitespace=True)
+    expected = DataFrame({"a": [1, 4], "b": [-2, 5], "c": [-3, 6]})
+    tm.assert_frame_equal(result, expected)
+
+
+def test_read_table_delim_whitespace_non_default_sep(all_parsers):
+    # GH: 35958
+    f = StringIO("a  b  c\n1 -2 -3\n4  5   6")
+    parser = all_parsers
+    msg = (
+        "Specified a delimiter with both sep and "
+        "delim_whitespace=True; you can only specify one."
+    )
+    with pytest.raises(ValueError, match=msg):
+        parser.read_table(f, delim_whitespace=True, sep=",")