Merge branch 'main' into api-timedelta-constructor

Author: jbrockmendel

.pre-commit-config.yaml

@@ -19,7 +19,7 @@ ci:
     skip: [pyright, mypy]
 repos:
 -   repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.14.3
+    rev: v0.14.7
     hooks:
     -   id: ruff
         args: [--exit-non-zero-on-fix]
@@ -71,7 +71,7 @@ repos:
     hooks:
     -   id: isort
 -   repo: https://github.com/asottile/pyupgrade
-    rev: v3.21.0
+    rev: v3.21.2
     hooks:
     -   id: pyupgrade
         args: [--py311-plus]
@@ -87,12 +87,12 @@ repos:
         types: [text]  # overwrite types: [rst]
         types_or: [python, rst]
 -   repo: https://github.com/sphinx-contrib/sphinx-lint
-    rev: v1.0.1
+    rev: v1.0.2
     hooks:
     - id: sphinx-lint
       args: ["--enable", "all", "--disable", "line-too-long"]
 -   repo: https://github.com/pre-commit/mirrors-clang-format
-    rev: v21.1.2
+    rev: v21.1.6
     hooks:
     - id: clang-format
       files: ^pandas/_libs/src|^pandas/_libs/include

doc/source/whatsnew/v3.0.0.rst

@@ -384,6 +384,8 @@ In cases with mixed-resolution inputs, the highest resolution is used:
 
 .. warning:: Many users will now get "M8[us]" dtype data in cases when they used to get "M8[ns]". For most use cases they should not notice a difference. One big exception is converting to integers, which will give integers 1000x smaller.
 
+Similarly, the :class:`Timedelta` constructor and :func:`to_timedelta` with a string input now defaults to a microsecond unit, using nanosecond unit only in cases that actually have nanosecond precision.
+
 .. _whatsnew_300.api_breaking.concat_datetime_sorting:
 
 :func:`concat` no longer ignores ``sort`` when all objects have a :class:`DatetimeIndex`
@@ -1277,7 +1279,8 @@ Groupby/resample/rolling
 - Bug in :meth:`Rolling.apply` for ``method="table"`` where column order was not being respected due to the columns getting sorted by default. (:issue:`59666`)
 - Bug in :meth:`Rolling.apply` where the applied function could be called on fewer than ``min_period`` periods if ``method="table"``. (:issue:`58868`)
 - Bug in :meth:`Rolling.sem` computing incorrect results because it divided by ``sqrt((n - 1) * (n - ddof))`` instead of ``sqrt(n * (n - ddof))``. (:issue:`63180`)
-- Bug in :meth:`Rolling.skew` incorrectly computing skewness for windows following outliers due to numerical instability. The calculation now properly handles catastrophic cancellation by recomputing affected windows (:issue:`47461`)
+- Bug in :meth:`Rolling.skew` and in :meth:`Rolling.kurt` incorrectly computing skewness and kurtosis, respectively, for windows following outliers due to numerical instability. The calculation now properly handles catastrophic cancellation by recomputing affected windows (:issue:`47461`, :issue:`61416`)
+- Bug in :meth:`Rolling.skew` and in :meth:`Rolling.kurt` where results varied with input length despite identical data and window contents (:issue:`54380`)
 - Bug in :meth:`Series.resample` could raise when the date range ended shortly before a non-existent time. (:issue:`58380`)
 - Bug in :meth:`Series.resample` raising error when resampling non-nanosecond resolutions out of bounds for nanosecond precision (:issue:`57427`)
 - Bug in :meth:`Series.rolling.var` and :meth:`Series.rolling.std` computing incorrect results due to numerical instability. (:issue:`47721`, :issue:`52407`, :issue:`54518`, :issue:`55343`)

pandas/_libs/tslibs/timedeltas.pyx

@@ -1,4 +1,5 @@
 import collections
+import re
 import warnings
 
 from pandas.util._decorators import set_module
@@ -448,11 +449,19 @@ def array_to_timedelta64(
                     ival = parse_iso_format_string(item)
                 else:
                     ival = parse_timedelta_string(item)
+                if (
+                    (infer_reso or creso == NPY_DATETIMEUNIT.NPY_FR_us)
+                    and not needs_nano_unit(ival, item)
+                ):
+                    item_reso = NPY_DATETIMEUNIT.NPY_FR_us
+                    ival = ival // 1000
+                else:
+                    item_reso = NPY_FR_ns
 
-                item_reso = NPY_FR_ns
-                state.update_creso(item_reso)
-                if infer_reso:
-                    creso = state.creso
+                if ival != NPY_NAT:
+                    state.update_creso(item_reso)
+                    if infer_reso:
+                        creso = state.creso
 
             elif is_tick_object(item):
                 item_reso = get_supported_reso(item._creso)
@@ -722,6 +731,24 @@ cdef timedelta_from_spec(object number, object frac, object unit):
     return cast_from_unit(float(n), unit)
 
 
+cdef bint needs_nano_unit(int64_t ival, str item):
+    """
+    Check if a passed string `item` needs to be stored with nano unit or can
+    use microsecond instead. Needs nanoseconds if:
+
+    - if the parsed value in nanoseconds has sub-microseconds content -> certainly
+      needs nano
+    - if the seconds part in the string contains more than 6 decimals, i.e. has
+      trailing zeros beyond the microsecond part (e.g. "0.123456000 s") -> treat
+      as nano for consistency
+    - if the string explicitly contains an entry for nanoseconds (e.g. "1000 ns")
+    """
+    # TODO: more performant way of doing this check?
+    if ival % 1000 != 0:
+        return True
+    return re.search(r"\.\d{7}", item) or "ns" in item or "nano" in item.lower()
+
+
 cpdef inline str parse_timedelta_unit(str unit):
     """
     Parameters
@@ -2128,10 +2155,17 @@ class Timedelta(_Timedelta):
             if (len(value) > 0 and value[0] == "P") or (
                 len(value) > 1 and value[:2] == "-P"
             ):
-                value = parse_iso_format_string(value)
+                ival = parse_iso_format_string(value)
+            else:
+                ival = parse_timedelta_string(value)
+
+            if not needs_nano_unit(ival, value):
+                # If we don't specifically need nanosecond resolution, default
+                #  to microsecond like we do for datetimes
+                value = np.timedelta64(ival // 1000, "us")
+                return cls(value)
             else:
-                value = parse_timedelta_string(value)
-            value = np.timedelta64(value)
+                value = np.timedelta64(ival, "ns")
         elif PyDelta_Check(value):
             # pytimedelta object -> microsecond resolution
             new_value = delta_to_nanoseconds(