ENH: ISO8601-compliant datetime string conversion in iterrows() and Series construction.

pandas/core/dtypes/cast.py

@@ -904,15 +904,19 @@ def maybe_infer_to_datetimelike(value, convert_dates=False):
     def try_datetime(v):
         # safe coerce to datetime64
         try:
-            v = tslib.array_to_datetime(v, errors='raise')
+            # GH19671
+            v = tslib.array_to_datetime(v,
+                                        require_iso8601=True,
+                                        errors='raise')
         except ValueError:
 
             # we might have a sequence of the same-datetimes with tz's
             # if so coerce to a DatetimeIndex; if they are not the same,
             # then these stay as object dtype
             try:
                 from pandas import to_datetime
-                return to_datetime(v)
+                # GH19671
+                return to_datetime(v, require_iso8601=True)
             except Exception:
                 pass
 

pandas/core/tools/datetimes.py

@@ -106,7 +106,7 @@ def _convert_and_box_cache(arg, cache_array, box, errors, name=None):
 def to_datetime(arg, errors='raise', dayfirst=False, yearfirst=False,
                 utc=None, box=True, format=None, exact=True,
                 unit=None, infer_datetime_format=False, origin='unix',
-                cache=False):
+                cache=False, **kwargs):
     """
     Convert argument to datetime.
 
@@ -272,8 +272,10 @@ def to_datetime(arg, errors='raise', dayfirst=False, yearfirst=False,
     from pandas.core.indexes.datetimes import DatetimeIndex
 
     tz = 'utc' if utc else None
+    require_iso8601 = kwargs.get('require_iso8601', None)
 
-    def _convert_listlike(arg, box, format, name=None, tz=tz):
+    def _convert_listlike(arg, box, format, name=None, tz=tz,
+                          require_iso8601=require_iso8601):
 
         if isinstance(arg, (list, tuple)):
             arg = np.array(arg, dtype='O')
@@ -313,11 +315,8 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
                             '1-d array, or Series')
 
         arg = _ensure_object(arg)
-        require_iso8601 = False
-
         if infer_datetime_format and format is None:
             format = _guess_datetime_format_for_array(arg, dayfirst=dayfirst)
-
         if format is not None:
             # There is a special fast-path for iso8601 formatted
             # datetime strings, so in those cases don't use the inferred

pandas/tests/dtypes/test_cast.py

@@ -300,6 +300,10 @@ def test_maybe_infer_to_datetimelike(self):
                                      [NaT, 'b', 1]]))
         assert result.size == 6
 
+        # GH19671
+        result = Series(['M1701', Timestamp('20130101')])
+        assert result.dtype.kind == 'O'
+
 
 class TestConvert(object):
 

pandas/tests/indexes/datetimes/test_tools.py

@@ -467,6 +467,22 @@ def test_datetime_bool(self, cache):
                                              NaT,
                                              to_datetime(0, cache=cache)]))
 
+    def test_datetime_require_iso8601(self):
+        # GH19671
+        s = Series(['M1809', 'M1701', Timestamp('20130101')])
+        with pytest.raises(ValueError):
+            to_datetime(s, require_iso8601=True, errors='raise')
+        tm.assert_series_equal(
+            to_datetime(s, require_iso8601=True, errors='ignore'),
+            Series(['M1809', 'M1701', Timestamp('20130101')]))
+        tm.assert_series_equal(
+            to_datetime(s, require_iso8601=True, errors='coerce'),
+            Series([NaT, NaT, Timestamp('20130101')]))
+        tm.assert_series_equal(
+            to_datetime(s, require_iso8601=False, errors='raise'),
+            Series([Timestamp('18090101'), Timestamp('17010101'),
+                    Timestamp('20130101')]))
+
     def test_datetime_invalid_datatype(self):
         # GH13176