[BUG] Add is_coerce argument to func array_to_datetime_object (GH26122)

doc/source/whatsnew/v0.25.0.rst

@@ -273,7 +273,7 @@ Datetimelike
 - Bug in :class:`DataFrame` and :class:`Series` where timezone aware data with ``dtype='datetime64[ns]`` was not cast to naive (:issue:`25843`)
 - Improved :class:`Timestamp` type checking in various datetime functions to prevent exceptions when using a subclassed ``datetime`` (:issue:`25851`)
 - Bug in :class:`Series` and :class:`DataFrame` repr where ``np.datetime64('NaT')`` and ``np.timedelta64('NaT')`` with ``dtype=object`` would be represented as ``NaN`` (:issue:`25445`)
--
+- Bug in :func:`to_datetime` which does not replace the invalid argument with ``NaT`` when error is set to coerce (:issue:`26122`)
 
 Timedelta
 ^^^^^^^^^

pandas/_libs/tslib.pyx

@@ -682,7 +682,8 @@ cpdef array_to_datetime(ndarray[object] values, str errors='raise',
         return ignore_errors_out_of_bounds_fallback(values), tz_out
 
     except TypeError:
-        return array_to_datetime_object(values, is_raise, dayfirst, yearfirst)
+        return array_to_datetime_object(values, errors,
+                                        dayfirst, yearfirst)
 
     if seen_datetime and seen_integer:
         # we have mixed datetimes & integers
@@ -697,7 +698,7 @@ cpdef array_to_datetime(ndarray[object] values, str errors='raise',
         elif is_raise:
             raise ValueError("mixed datetimes and integers in passed array")
         else:
-            return array_to_datetime_object(values, is_raise,
+            return array_to_datetime_object(values, errors,
                                             dayfirst, yearfirst)
 
     if seen_datetime_offset and not utc_convert:
@@ -709,7 +710,7 @@ cpdef array_to_datetime(ndarray[object] values, str errors='raise',
         #    (with individual dateutil.tzoffsets) are returned
         is_same_offsets = len(out_tzoffset_vals) == 1
         if not is_same_offsets:
-            return array_to_datetime_object(values, is_raise,
+            return array_to_datetime_object(values, errors,
                                             dayfirst, yearfirst)
         else:
             tz_offset = out_tzoffset_vals.pop()
@@ -757,7 +758,7 @@ cdef inline ignore_errors_out_of_bounds_fallback(ndarray[object] values):
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-cdef array_to_datetime_object(ndarray[object] values, bint is_raise,
+cdef array_to_datetime_object(ndarray[object] values, str errors,
                               bint dayfirst=False, bint yearfirst=False):
     """
     Fall back function for array_to_datetime
@@ -769,7 +770,7 @@ cdef array_to_datetime_object(ndarray[object] values, bint is_raise,
     ----------
     values : ndarray of object
          date-like objects to convert
-    is_raise : bool
+    errors : str, default 'raise'
          error behavior when parsing
     dayfirst : bool, default False
          dayfirst parsing behavior when encountering datetime strings
@@ -783,9 +784,14 @@ cdef array_to_datetime_object(ndarray[object] values, bint is_raise,
     cdef:
         Py_ssize_t i, n = len(values)
         object val,
+        bint is_ignore = errors == 'ignore'
+        bint is_coerce = errors == 'coerce'
+        bint is_raise = errors == 'raise'
         ndarray[object] oresult
         npy_datetimestruct dts
 
+    assert is_raise or is_ignore or is_coerce
+
     oresult = np.empty(n, dtype=object)
 
     # We return an object array and only attempt to parse:
@@ -806,6 +812,9 @@ cdef array_to_datetime_object(ndarray[object] values, bint is_raise,
                 pydatetime_to_dt64(oresult[i], &dts)
                 check_dts_bounds(&dts)
             except (ValueError, OverflowError):
+                if is_coerce:
+                    oresult[i] = NaT
+                    continue
                 if is_raise:
                     raise
                 return values, None

pandas/tests/indexes/datetimes/test_tools.py

@@ -712,6 +712,19 @@ def test_week_without_day_and_calendar_year(self, date, format):
         with pytest.raises(ValueError, match=msg):
             pd.to_datetime(date, format=format)
 
+    def test_to_datetime_coerce(self):
+        # GH 26122
+        ts_strings = ['March 1, 2018 12:00:00+0400',
+                      'March 1, 2018 12:00:00+0500',
+                      '20100240']
+        result = to_datetime(ts_strings, errors='coerce')
+        expected = Index([datetime(2018, 3, 1, 12, 0,
+                                   tzinfo=tzoffset(None, 14400)),
+                          datetime(2018, 3, 1, 12, 0,
+                                   tzinfo=tzoffset(None, 18000)),
+                          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"