PERF: check first for recognized scalars in DatetimeArray._validate_scalar (#44608)

Author: jorisvandenbossche

pandas/core/arrays/datetimelike.py

@@ -635,7 +635,10 @@ def _validate_scalar(
  -------
  self._scalar_type or NaT
  """
- if isinstance(value, str):
+ if isinstance(value, self._scalar_type):
+ pass
+
+ elif isinstance(value, str):
  # NB: Careful about tzawareness
  try:
  value = self._scalar_from_string(value)

pandas/core/arrays/datetimes.py

@@ -508,7 +508,7 @@ def _check_compatible_with(self, other, setitem: bool = False):
  self._assert_tzawareness_compat(other)
  if setitem:
  # Stricter check for setitem vs comparison methods
- if not timezones.tz_compare(self.tz, other.tz):
+ if self.tz is not None and not timezones.tz_compare(self.tz, other.tz):
  # TODO(2.0): remove this check. GH#37605
  warnings.warn(
  "Setitem-like behavior with mismatched timezones is deprecated "