REF: re-use objects_to_datetime64ns in maybe_infer_to_datetimelike (#40120)

Author: jbrockmendel

pandas/core/arrays/timedeltas.py

@@ -4,6 +4,7 @@
 from typing import (
     List,
     Optional,
+    Tuple,
     Union,
 )
 
@@ -907,7 +908,9 @@ def f(x):
 # Constructor Helpers
 
 
-def sequence_to_td64ns(data, copy=False, unit=None, errors="raise"):
+def sequence_to_td64ns(
+    data, copy=False, unit=None, errors="raise"
+) -> Tuple[np.ndarray, Optional[Tick]]:
     """
     Parameters
     ----------

pandas/core/dtypes/cast.py

@@ -1416,31 +1416,43 @@ def maybe_infer_to_datetimelike(value: Union[np.ndarray, List]):
         return value
 
     def try_datetime(v: np.ndarray) -> ArrayLike:
-        # safe coerce to datetime64
-        try:
-            # GH19671
-            # tznaive only
-            v = tslib.array_to_datetime(v, require_iso8601=True, errors="raise")[0]
-        except ValueError:
+        # Coerce to datetime64, datetime64tz, or in corner cases
+        #  object[datetimes]
+        from pandas.core.arrays.datetimes import (
+            DatetimeArray,
+            objects_to_datetime64ns,
+            tz_to_dtype,
+        )
 
+        try:
+            # GH#19671 we pass require_iso8601 to be relatively strict
+            #  when parsing strings.
+            vals, tz = objects_to_datetime64ns(
+                v,
+                require_iso8601=True,
+                dayfirst=False,
+                yearfirst=False,
+                allow_object=True,
+            )
+        except (ValueError, TypeError):
+            # e.g. <class 'numpy.timedelta64'> is not convertible to datetime
+            return v.reshape(shape)
+        else:
             # 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, xref GH19671
-            from pandas import DatetimeIndex
-
-            try:
-
-                values, tz = conversion.datetime_to_datetime64(v)
-            except (ValueError, TypeError):
-                pass
-            else:
-                dti = DatetimeIndex(values).tz_localize("UTC").tz_convert(tz=tz)
-                return dti._data
-        except TypeError:
-            # e.g. <class 'numpy.timedelta64'> is not convertible to datetime
-            pass
-
-        return v.reshape(shape)
+            # then these stay as object dtype, xref GH#19671
+
+            if vals.dtype == object:
+                # This is reachable bc allow_object=True, means we cast things
+                #  to mixed-tz datetime objects (mostly).  Only 1 test
+                #  relies on this behavior, see GH#40111
+                return vals.reshape(shape)
+
+            dta = DatetimeArray._simple_new(vals.view("M8[ns]"), dtype=tz_to_dtype(tz))
+            if dta.tz is None:
+                # TODO(EA2D): conditional reshape kludge unnecessary with 2D EAs
+                return dta._ndarray.reshape(shape)
+            return dta
 
     def try_timedelta(v: np.ndarray) -> np.ndarray:
         # safe coerce to timedelta64