BUG: Fix to_datetime(errors='coerce') not swallowing all parser exceptions...

doc/source/whatsnew/v1.0.0.rst

@@ -115,10 +115,10 @@ Datetimelike
 - Bug in :meth:`Series.__setitem__` incorrectly casting ``np.timedelta64("NaT")`` to ``np.datetime64("NaT")`` when inserting into a :class:`Series` with datetime64 dtype (:issue:`27311`)
 - Bug in :meth:`Series.dt` property lookups when the underlying data is read-only (:issue:`27529`)
 - Bug in ``HDFStore.__getitem__`` incorrectly reading tz attribute created in Python 2 (:issue:`26443`)
+- Bug in :func:`to_datetime` where passing arrays of malformed ``str`` while attempting to coerce errors could incorrectly lead to raising errors instead (:issue:`28299`)
 - Bug in :meth:`pandas.core.groupby.SeriesGroupBy.nunique` where ``NaT`` values were interfering with the count of unique values (:issue:`27951`)
 - Bug in :class:`Timestamp` subtraction when subtracting a :class:`Timestamp` from a ``np.datetime64`` object incorrectly raising ``TypeError`` (:issue:`28286`)
 - Addition and subtraction of integer or integer-dtype arrays with :class:`Timestamp` will now raise ``NullFrequencyError`` instead of ``ValueError`` (:issue:`28268`)
--
 
 
 Timedelta

pandas/_libs/tslib.pyx

@@ -609,16 +609,17 @@ cpdef array_to_datetime(ndarray[object] values, str errors='raise',
                             py_dt = parse_datetime_string(val,
                                                           dayfirst=dayfirst,
                                                           yearfirst=yearfirst)
+                            # If the dateutil parser returned tzinfo, capture it
+                            # to check if all arguments have the same tzinfo
+                            tz = py_dt.utcoffset()
+
                         except Exception:
                             if is_coerce:
                                 iresult[i] = NPY_NAT
                                 continue
                             raise TypeError("invalid string coercion to "
                                             "datetime")
 
-                        # If the dateutil parser returned tzinfo, capture it
-                        # to check if all arguments have the same tzinfo
-                        tz = py_dt.utcoffset()
                         if tz is not None:
                             seen_datetime_offset = 1
                             # dateutil timezone objects cannot be hashed, so

pandas/tests/indexes/datetimes/test_tools.py

@@ -901,6 +901,13 @@ def test_to_datetime_coerce(self):
         )
         tm.assert_index_equal(result, expected)
 
+    def test_to_datetime_coerce_malformed(self):
+        # GH 28299
+        ts_strings = ["200622-12-31", "111111-24-11"]
+        result = to_datetime(ts_strings, errors="coerce")
+        expected = Index([NaT, NaT])
+        tm.assert_index_equal(result, expected)
+
     def test_iso_8601_strings_with_same_offset(self):
         # GH 17697, 11736
         ts_str = "2015-11-18 15:30:00+05:30"