[BUG]: Fix regression in read_table with delim_whitespace=True

doc/source/whatsnew/v1.1.3.rst

@@ -39,6 +39,7 @@ 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`)
 
 .. ---------------------------------------------------------------------------

pandas/io/parsers.py

@@ -757,6 +757,16 @@ 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())
 
 

pandas/tests/io/parser/test_common.py

@@ -2200,3 +2200,24 @@ 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=",")