CLN: non-nano follow-ups (#47682)

Author: jbrockmendel

pandas/_libs/tslib.pyx

@@ -152,7 +152,7 @@ def format_array_from_datetime(
  # a format based on precision
  basic_format = format is None
  if basic_format:
- reso_obj = get_resolution(values, reso=reso)
+ reso_obj = get_resolution(values, tz=tz, reso=reso)
  show_ns = reso_obj == Resolution.RESO_NS
  show_us = reso_obj == Resolution.RESO_US
  show_ms = reso_obj == Resolution.RESO_MS

pandas/_libs/tslibs/conversion.pyx

@@ -144,9 +144,13 @@ cpdef inline (int64_t, int) precision_from_unit(str unit):
  NPY_DATETIMEUNIT reso = abbrev_to_npy_unit(unit)
 
  if reso == NPY_DATETIMEUNIT.NPY_FR_Y:
+ # each 400 years we have 97 leap years, for an average of 97/400=.2425
+ # extra days each year. We get 31556952 by writing
+ # 3600*24*365.2425=31556952
  m = 1_000_000_000 * 31556952
  p = 9
  elif reso == NPY_DATETIMEUNIT.NPY_FR_M:
+ # 2629746 comes from dividing the "Y" case by 12.
  m = 1_000_000_000 * 2629746
  p = 9
  elif reso == NPY_DATETIMEUNIT.NPY_FR_W:

pandas/_libs/tslibs/vectorized.pyi

@@ -42,5 +42,5 @@ def ints_to_pydatetime(
 def tz_convert_from_utc(
  stamps: npt.NDArray[np.int64],
  tz: tzinfo | None,
- reso: int = ...,
+ reso: int = ..., # NPY_DATETIMEUNIT
 ) -> npt.NDArray[np.int64]: ...

pandas/core/indexes/base.py

@@ -6897,6 +6897,7 @@ def insert(self, loc: int, item) -> Index:
 
  # Use self._constructor instead of Index to retain NumericIndex GH#43921
  # TODO(2.0) can use Index instead of self._constructor
+ # Check if doing so fixes GH#47071
  return self._constructor._with_infer(new_values, name=self.name)
 
  def drop(